The total of contributions under the last sentence of section 5170c of this title for the insular areas shall not exceed 10 percent of the estimated aggregate amounts of grants to be made under sections 5170b, 5172, 5173, 5174, and 5178 ¹ of this title for any disaster: Provided, That the President shall require a 50 percent local match for assistance in excess of 10 percent of the estimated aggregate amount of grants to be made under section 5172 of this title for any disaster.