In favour of a class being made smaller (3)

I believe the answer is:

for

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'in favour of' is the definition.
(being for a particular cause)

I cannot understand how the remainder of the clue works.

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(Other definitions for for that I've seen before include "Favouring" , "In support of" , "and 16 and 20: Notwithstanding" , "In favour of; since" , "On behalf of" .)

I've seen this clue in The Irish News.

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