The amount of each monthly allowance paid since May 19, 1977, as specified in NRS 286.673 to 286.677, inclusive, shall not exceed the deceased member’s average compensation and shall be reduced by the amount of any other benefit received from any source:
1. If that benefit was provided or purchased by the expenditure of money by a public employer in this state, except for lump-sum payments under a group insurance program; and
2. To the extent that the total of the allowance and the other benefit would otherwise exceed the deceased member’s average compensation.