Shifting apart or in proportion

I believe the answer is:

prorata

'in proportion' is the definition.
(I've seen this before)

'shifting apart or' is the wordplay.
'shifting' indicates anagramming the letters.
'apart'+'or'='apartor'
'apartor' anagrammed gives 'PRO RATA'.

(Another definition for prorata that I've seen is " according to mathematical requirements".)

I've seen this clue in The Daily Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.