any periods of service as a border patrol agent prior to the first day of the first pay period beginning on or after January 1, 2016, shall be included, and the agent’s assigned overtime supplement during such periods shall be deemed to be 25 percent. (4) Annual leave payment For the purpose of computing an agent’s lump-sum annual leave payment under section 5551 or 5552, the pay the agent is projected to receive shall include a deemed overtime supplement derived under this paragraph. Such overtime supplement shall be based on the lower of the agent’s actual overtime supplement percentage in effect at separation or the average percentage of the agent’s overtime supplement over the 26 full biweekly pay periods immediately preceding that separation, and shall not exceed the amount that is or would be payable under the premium pay limitation in section 5547.