At issue in this declaratory judgment action is the interpretation under Kansas law of an umbrella insurance policy1 issued by defendant-appellants California Union Insurance Company (“Cal Union”) and Indemnity Insurance Company of North America (“Indico”) to plaintiff-appellee The Coleman Company, Inc. (“Coleman”).2 Specifically, we must determine whether defense costs incurred by the insured, Coleman, which are clearly included in calculating the limit of liability of the underlying policy, are also included in calculating the attachment point of the umbrella policy. On cross-motions for summary judgment, the district court construed the policy as ambiguous, and held that, under Kansas law, the policy must be interpreted against Cal Union. Our jurisdiction arises under 28 U.S.C. § 1291, and our review is de *1531novo. Hocker v. New Hampshire Ins. Co., 922 F.2d 1476, 1480 (10th Cir. 1991). While we do not agree with the district court that the umbrella policy is ambiguous, we affirm the district court’s order because the terms of the policy unambiguously support Coleman’s construction. See Scivally v. Time Ins. Co., 724 F.2d 101, 103 (10th Cir. 1983) (“trial court’s decision will be affirmed if the record reveals another ground which supports the decision”).

While the umbrella policy at issue in this case was for the years 1980-85, a discussion of the circumstances leading to an earlier excess policy for the years 1978-79 is helpful in understanding the source of this dispute and the parties’ knowledge in entering into the disputed insurance contract. In 1977, third-party-defendant Insurance Management Associates (“IMA”), a retail insurance broker, proposed a liability insurance plan to Coleman, a manufacturer of recreational and household goods. The plan provided that Coleman would retain primary coverage of $2.5 million, to include losses and expenses, after which umbrella liability coverage would attach. IMA contacted defendant and third-party-plaintiff Avreco Inc., a wholesale insurance broker, which, in turn contacted Cal Union about obtaining umbrella coverage for Coleman. Avreco submitted materials it had received from IMA to Cal Union, see Aplee.App. 1-97, including a proposed underlying comprehensive general liability (“CGL”) policy which included defense costs in its limits of liability.3 See id. at 37.

Cal Union initially declined to write umbrella coverage for Coleman, but after two subsequent inquiries by Avreco, Cal Union “indicate[d]” that it would write an excess policy “to follow Commercial Union primary which [sic] standard CGL/Products form.”4 Aplts.App. at 375. Avreco responded with a “firm order to bind and issue coverage_” Id. at 376. The following day, Cal Union communicated to Avreco that the excess policy was binding as of January 1, 1978, and that a copy of the underlying policy was required. Aplee. App. at 98. Three months later, the underlying policy, which included defense costs within the policy limits, was sent to Cal Union. See id. at 99-135, 107. Cal Union subsequently drafted an endorsement to the 1978 excess policy stating that an obligation to defend was not within the excess policy’s coverage.5 Cal Union then issued the 1978 excess policy, and an identical policy was issued for 1979.

With this background in mind, we address the policy at issue. Beginning in 1980 and continuing through 1985, Cal Union issued an umbrella policy which is different from the 1978-79 excess policy.6 In *1532interpreting this policy, we must “consider the instrument as a whole and endeavor to ascertain the intention of the parties from the language used, taking into account the situation of the parties, the nature of the subject matter and the purpose to be accomplished.” American Media, Inc. v. Home Indem. Co., 232 Kan. 737, 658 P.2d 1015, 1018 (1983); Mah v. United States Fire Ins. Co., 218 Kan. 583, 545 P.2d 366, 369 (1976); Bramlett v. State Farm Mut. Auto. Ins. Co., 205 Kan. 128, 468 P.2d 157, 159 (1970). The umbrella policy must be “construed according to the sense and meaning of the terms used, and if the language is clear and unambiguous, it must be taken in its plain, ordinary and popular sense_” American Media, 658 P.2d at 1018; Mah, 545 P.2d at 369; Bramlett, 468 P.2d at 159. “The test to be applied in determining the intention of the parties ... is not what the insurer intended the policy to mean, but what a reasonable person in the position of the insured would understand it to mean.”7 American Media, 658 P.2d at 1019; Fancher v. Carson-Campbell, Inc., 216 Kan. 141, 530 P.2d 1225, 1229 (1975). See also St. Paul Fire & Marine v. Medical Protective Co., 691 F.2d 468, 470 (10th Cir. 1982).

The “Insuring Agreement” of the umbrella policy provides that Cal Union

*1533will indemnify [Coleman] for ultimate net loss in excess of the retained limit hereinafter stated which [Coleman] shall become legally obligated to pay as damages because of [¶] A. personal injury [If] B. property damage [11] C. advertising injury [II] to which this insurance applies, caused by an occurrence....

Aplts. Brief, ex. B. The “Insuring Agreement” also imposes a “duty” on Cal Union to defend

[w]ith respect to any personal injury, property damage or advertising injury not within the terms of coverage of underlying insurance but within the terms of coverage of this insurance, or [if] [i]f the limits of liability of the underlying insurance are exhausted because of personal injury, property damage or advertising injury....

Id. Costs incurred by Cal Union in defending Coleman are “in addition to the amount of ultimate net loss payable....” Id.

As Cal Union’s duty to indemnify for “ultimate net loss” is triggered when the “retained limit” is exceeded, the critical definition in calculating the attachment point of the umbrella policy is “retained limit.” This term is defined in a separate section entitled “Retained Limit — The Company’s Limit of Liability.” This section provides that Cal Union’s “liability is limited ... [to] the ultimate net loss in excess of [Coleman’s] retained limit....” Id. “Retained limit” is then defined, in relevant part, as

an amount equal to the limits of liability indicated beside the underlying insurance listed in Schedule A hereof, plus the applicable limits of any other underlying insurance collectible by [Coleman].

Id. Schedule A, in turn, lists the underlying insurance carrier, the underlying policy by number, and the limit of liability, per occurrence and in the aggregate, on the underlying policy.

Coleman continues to maintain that the umbrella policy unambiguously provides that defense costs are included in calculating the attachment point. Coleman argues that the policy’s definition of “retained limit” which directs the reader to a specific underlying policy in Schedule A unambiguously incorporates the manner by which the underlying policy’s limit of liability is calculated in order to calculate the retained limit of the umbrella policy. Given that the underlying policy clearly includes defense costs in its limit of liability, such costs should also be included in determining the retained limit of the umbrella policy.

We agree with the district court that this section “does nothing, explicitly or implicitly, to ‘incorporate’ the terms of the underlying policy.” Coleman Co. v. California Union Ins. Co., No. 87-1700-K, slip op. at 16, 1990 WL 146513 (D.Kan. Sept. 6, 1990). The use of the language “amount equal to the limits of liability indicated beside the underlying insurance listed in Schedule A hereof,” as opposed to language such as “as provided by” or “as contained in” expresses a “manifest intent and effect of this provision ... simply to allow the insurer and insured to designate the total amount of the limits of liability in a separate schedule.” Id. at 16-17. Indeed, Coleman’s construction reads out the phrases “amount equal to” and “indicated beside.” Because we must construe the policy “from the sense and meaning of the terms used,” we cannot read out this language. Therefore, the definition of “retained limit” simply indicates that it is an amount as indicated in Schedule A, and gives us no guidance on how to calculate this amount.

Coleman’s construction of the umbrella policy, however, is supported by an endorsement which provides that “coverage” under the umbrella policy “shall follow and be subject to the same terms and conditions of the underlying policy....”8 In Home *1534Ins. Co. v. American Home Products Corp., 902 F.2d 1111 (2d Cir. 1990), the court recognized that a similar “following form” agreement subjected the excess insurer to the same “ ‘terms conditions and exclusions’ ” of the underlying policy.9 Id. at 1113. Similarly, in Juntunen v. Sea-Con Services, Inc., 879 F.2d 154, 156 (5th Cir. 1989), the court interpreted a similar provision stating that the excess policy “shall follow the terms, conditions, definitions and exclusions of the controlling underlying policy” as permitting the excess insurer to reduce its limit of liability by the amount of attorney fees and defense costs it incurred because the underlying policy excluded attorney fees. Id. at 155-56. In King v. Employers Nat’l Ins. Co., 928 F.2d 1438 (5th Cir. 1991), the court relied on a similar provision and looked to the underlying policy in which a company was “additional insured” to determine whether the company was an “other insured” under the excess policy. Id. at 1444-45. These cases clearly support Coleman’s contention that the endorsement manifests an intent to consider the underlying policy in determining the coverage under the umbrella policy.

Given that the manner by which to calculate the “retained limit” is not set forth in the terms of the umbrella policy purporting to define “retained limit,” we believe that a reasonable insured in Coleman’s position would interpret the endorsement as providing that the manner by which the “retained limit” is calculated is determined by reference to the limit of liability of the underlying policy. This interpretation is consistent with the purpose of excess insurance, of which umbrella insurance is a type, which is to provide coverage where primary insurance ends. See Steve D. Thompson Trucking Co. v. Twin City Fire Ins., 832 F.2d 309, 310 (5th Cir. 1987) (per curiam). See generally Michael M. Marick, Excess Insurance: An Overview of General Principles and Current Issues, 24 Tort & Ins. L.J. 715, 717-19 (1989). Absent an expression of intent not to look to the underlying policy in order to calculate the “retained limit” of the umbrella policy, such incorporation is mandated by the express terms of the endorsement to the umbrella policy.

Cal Union directs us to the language from the “Insuring Agreement” section of the policy stating that Cal Union “will in*1535demnify [Coleman] for ultimate net loss in excess of the retained limit hereinafter stated which [Coleman] shall become legally obligated to pay as damages....” Cal Union construes the emphasized phrase as modifying “retained limit” and, therefore, contends that the umbrella coverage did not commence until Coleman paid the “retained limit” as damages. The district court agreed with this construction stating that this provision “makes clear that this ‘excess’ is the amount over and above the retained limit of those sums Coleman is ‘legally obligated to pay as damages/ rather than any sums (including defense costs) which Coleman may expend in connection with such claims.” 10 Coleman, No. 87-1700-K, slip op. at 12.

We do not agree with Cal Union and the district court’s construction. First, this construction ignores the language “hereinafter stated,” which immediately follows “retained limit” and which, in our view, directs the reader to the section entitled “Retained Limit — The Company’s Limit of Liability.” Second, this construction overlooks the phrase “to which this insurance applies” immediately following the list of the type of damages that are covered by the umbrella policy. Accordingly, the term “damages” is specifically defined in the umbrella policy as “only those damages which are payable because of personal injury, property damage or advertising injury to which this insurance applies....” In light of these factors and given that the phrase on which Cal Union’s argument hangs is found in the “Insuring Agreement” section of the policy, a more reasonable construction is that the emphasized phrase modifies “ultimate net loss,” thereby limiting coverage under the umbrella policy to that which Coleman “shall be legally obligated to pay as damages.”11

Additionally, Cal Union points to the umbrella policy’s condition entitled “Maintenance of Underlying Policies.” This condition imposes an obligation on Coleman to maintain the underlying policy and limits Cal Union’s liability, in the event that the underlying policy is not maintained, to that which it would have incurred had Coleman maintained the underlying policy. Specifically, this condition provides that Coleman

shall maintain the underlying policies (and renewals thereof) with limits of liability as stated in Schedule A in full effect during this policy period, except for any reduction or exhaustion of the aggregate limit or limits contained in such policies solely by payment of claims arising out of occurrences which happen during this policy period.

Aplts. Brief, ex. B. Cal Union contends that the emphasized language provides that the underlying policy can only be reduced or exhausted by “payment of claims” which it construes as limited to damages paid to third parties. However, this section does not purport to define the attachment point of the umbrella policy; the emphasized language simply modifies an exception to Coleman’s duty to maintain the underlying policy. Additionally, neither the umbrella policy nor the underlying policy defines “claims.” Under a standard liability policy, which imposes separate duties on the insurer to indemnify and defend and does not include defense costs in the limits of liability, “claims” may be typically understood as damages to third parties. However, under a nonstandard policy in which the duty to defend is not a separate obligation and defense costs are included within the limits of liability as in the underlying policy here, a reasonable insured could understood “claims” to encompass defense costs. Nevertheless, under no stretch of the imagination does Cal Union’s reference to an undefined term (modifying an exception to a condition) clearly and explicitly reveal Cal Union’s asserted *1536purpose of limiting the definition of “retained limit” — a term to which an entire separate section of the policy is devoted. See Krug v. Millers’ Mut. Ins. Ass’n, 209 Kan. 111, 495 P.2d 949, 954 (1972) (insurer assumes a duty to define limitations on coverage in clear and explicit terms); Goforth v. Franklin Life Ins. Co., 202 Kan. 413, 449 P.2d 477, 481 (1969) (insurer must use “clear and unambiguous language” to restrict coverage).

Cal Union asserts that had the parties intended to include pre-attachment defense costs in determining retained limit of the umbrella policy, Cal Union would have charged substantially higher premiums or would have increased the attachment point. Cal Union’s subjective intention is simply not relevant. See St. Paul Fire, 691 F.2d at 470; Clayton v. Alliance Mut. Cas. Co., 212 Kan. 640, 512 P.2d 507, 512 (1973). Cal Union further attempts to cloud the issue by an erroneous reliance on parole evidence concerning the negotiations leading to the 1978 excess policy. Notwithstanding that the evidence of the parties’ intent is not as clear as Cal Union would like us to believe, we will not consider such evidence because we do not view the policy as ambiguous. Furthermore, Kansas has clearly developed rules for interpreting insurance policies; these rules do not include consideration of extrinsic evidence. Nonetheless, Cal Union’s arguments are contradicted by its course of performance in 1984, 1985 and 1986, as it repeatedly recognized coverage for Coleman’s claims under the 1978 excess policy which applied only if defense costs were included in determining the attachment point.12

In Harnischfeger Corp. v. Harbor Ins. Co., 927 F.2d 974 (7th Cir.), cert. denied, — U.S. -, 112 S.Ct. 189, 116 L.Ed.2d 150 (1991), the Seventh Circuit interpreted an excess policy as not including pre-attachment defense costs in determining whether the underlying limits had been reached. Id. at 975-76. The underlying policy in Hamischfeger, like the underlying policy here, included defense costs in the limit of the underlying insurer’s obligation.13 Id. at 975. However, nothing in Hamischfeger indicates that coverage under the excess policy would follow the terms and conditions of the underlying policy. Moreover, the excess policy in Har-nischfeger did not purport to define its attachment point but rather merely stated that it “ ‘shall not attach unless and until [Hamischfeger or its insurer] shall have paid the amount of the underlying limits on account of such occurrence.’ ” Id. at 974. Thus, the court construed the attachment point as it is typically understood in the insurance business as meaning “sums paid to claimants, and not the insured’s out-of-pocket expenses.” Id. at 975. Thus, while the Hamischfeger court stated that “[n]o (sane) insurer would give its insured ... an option” of counting anything it put in its underlying policy’s limits against the attachment point of the excess policy, the express terms of the umbrella policy before us distinguish this case.

While we do not doubt that the standard practice in the insurance business is that pre-attachment defense costs are generally not included in determining the attachment point of an excess policy, we believe that excess insurers and insureds generally look to the underlying policy to determine *1537whether its limit of liability has been exhausted in determining whether the excess policy attaches. See Mead Reinsurance v. Granite State Ins. Co., 873 F.2d 1185, 1188 (9th Cir. 1989) (excess insurer’s liability determined by reference to underlying policy’s definition of “ultimate net loss”). While the source of this dispute appears to be that the underlying policy here is not a standard policy, as it includes defense costs in determining whether its limit of liability has been exhausted, we cannot fall back on the standard expectations of an insurer when the insured’s underlying policy specifically states something different. Cal Union had the underlying policy, and indeed requested it before issuing any policy. After receiving it, Cal Union added an endorsement relating to its obligation to defend after the policy had attached. Cal Union could have easily expressed its subjective intent that defense costs were not to be included in determining the attachment point of the policy. Thus, notwithstanding Cal Union’s claim that Coleman is receiving a windfall, we cannot ignore the plain language of the policy endorsement. Because the manner by which to calculate the “retained limit” is left otherwise undefined, the endorsement providing that coverage “shall follow and be subject to the same terms and conditions of the underlying policy” manifests the parties’ intent to look to the underlying policy to determine whether its limit of liability has been reached and, accordingly, whether the “retained limit” of the umbrella policy has been exceeded. Given that the underlying policy clearly includes defense costs in its limit of liability, defense costs must also be included in determining the attachment point of the umbrella policy.

This brings us to Cal Union’s final argument, that it is entitled to reformation due to mutual mistake. Kansas recognizes that an insurance policy, like any contract, may be reformed due to mutual mistake. See Stamps v. Consolidated Underwriters, 205 Kan. 187, 468 P.2d 84, 94 (1970); New York Life Ins. Co. v. Dickensheets, 165 Kan. 159, 193 P.2d 649, 654 (1948). A unilateral mistake is not sufficient as “both parties [must have] understood that the real agreement was what [the party seeking reformation] alleges it to be, but had unintentionally prepared and executed one which did not express the true agreement.” New York Life, 193 P.2d at 654 (internal quotations omitted). Reformation “can never be employed to make a new contract or to supply terms upon which the minds of the parties never met.” Waddle v. Bird, 122 Kan. 716, 253 P. 576, 577 (1927). The party seeking reformation has the burden of proving by clear and convincing evidence that the contract does not set forth the true intent of the parties. Id.

The district court did not address this claim; nevertheless, we do not believe that Cal Union has made a sufficient showing to defeat Coleman’s motion for summary judgment. Cal Union claims that the initial agreement on the 1978 excess policy between it and Avreco was that defense costs were not to be included in determining the attachment point of the excess policy. Cal Union also asserts that its premiums did not account for defense costs being included in the attachment point. As to the latter point, while it may indicate that Cal Union operated under a mistake about the terms of the policy, it does not raise an issue as to Coleman’s intent. Similarly, the circumstances surrounding the initial agreement with Avreco on the 1978 excess policy do not raise a genuine issue of material fact. These circumstances indicate, if anything, that the parties each operated under a different understanding of the underlying policy which the excess policy was to follow. By indicating to Avreco that its excess policy was to follow a “standard” CGL policy, Cal Union believed that the underlying policy would not include defense costs in its limit of liability. Nevertheless, Cal Union had the proposed underlying policy, and specifically identified the underlying insurer when it indicated it would provide excess coverage. Avreco obviously knew that the underlying policy included defense costs in its limit of liability because it supplied the policy to Cal Union as demanded prior to the issuance of the excess policy. These facts do not raise a genuine issue of material fact as to *1538whether Avreco did not intend the umbrella policy to include defense costs in calculating its attachment point. Indeed, it is undisputed that IMA instructed Avreco to obtain “following form” coverage. At best, these facts indicate that Cal Union was unilaterally mistaken in its belief that the underlying policy did not include defense costs in its limit of liability. Cal Union has not presented a genuine issue of material fact concerning Coleman’s intent sufficient to permit a reasonable fact finder to return a verdict for Cal Union on the reformation issue. Therefore, Cal Union cannot defeat summary judgment by claiming it is entitled to reformation. See Anderson v. Liberty Lobby, Inc., 477 U.S. 242, 248, 106 S.Ct. 2505, 2510, 91 L.Ed.2d 202 (1986).

AFFIRMED.