The Secretary shall pay each month to each Spanish-American War veteran who is receiving, or entitled to receive, pension based on a need of regular aid and attendance, whichever amount is greater (i) that provided by subparagraph (B) of subsection (a)(1) of this section, or (ii) that which is payable to the veteran under
section 1521 of this title as in effect on
December 31, 1978, under regulations which the Secretary shall prescribe. Each change in the amount of pension payment required by this subparagraph shall be effective as of the first day of the month during which the facts of the particular case warrant such change, and shall be made without specific application therefor.