The amount of an annual payment under this subchapter is equal to the difference between:
(1) any amount received by the peace officer for the injury or disability from another source of income, including settlements related to the injury or disability, insurance benefits, federal disability benefits, workers’ compensation benefits, and benefits from another governmental entity, if those amounts do not exceed the amount described by Subdivision (2); and
(2) an amount equal to the officer’s average annual salary during the officer’s final three years as a peace officer.