(1) The payment shall be based on the unpaid mortgage balance(s) on the displacement dwelling; however, in the event the displaced person obtains a smaller mortgage than the mortgage balance(s) computed in the buydown determination, the payment will be prorated and reduced accordingly. (See appendix A, § 24.401(d).) In the case of a home equity loan the unpaid balance shall be that balance which existed 180 days prior to the initiation of negotiations or the balance on the date of acquisition, whichever is less.