Subject to paragraph (2), the amount of any increase under subsection (a) in the minimum rate for any grade may not (except in the case of nurse anesthetists, licensed practical nurses, licensed vocational nurses, nursing positions otherwise covered by title 5, pharmacists, and licensed physical therapists) exceed the maximum rate of basic pay (excluding any locality-based comparability payment under
section 5304 of title 5 or similar provision of law) for the grade or level by more than 50 percent.