If the amount appropriated under section
300x–35
(a) of this title for a fiscal year is equal to or less than the amount appropriated under such section for the prior fiscal year, the amount of the State allotment under section
300x–21 of this title shall be equal to the amount that the State received under section
300x–21 of this title in the prior fiscal year decreased by the percentage by which the amount appropriated for such fiscal year is less than the amount appropriated or such section for the prior fiscal year.