“ If the amount appropriated pursuant to section 399 (a) (2) (A) for any fiscal year is not sufficient to pay the minimum allotment required by paragraph (1) to all part B institutions, the amount of such minimum allotments shall be ratably reduced. If additional sums become available for such fiscal year, such reduced allocations shall be increased on the same basis as the basis on which they were reduced (until the amount allotted equals the minimum allotment required by paragraph (1) ) . ”