Most expansive point I would put in (6)
I believe the answer is:
widest
'most expansive' is the definition.
(I've seen this in another clue)
'point i would put in' is the wordplay.
'point' becomes 'west' (west is a kind of point).
'i would' becomes 'I'd'.
'put in' is an insertion indicator.
'west' placed around 'id' is 'WIDEST'.
(Other definitions for widest that I've seen before include "Broadest" , "most spacious" , "showing maximal gap between sides" , "most unplayable for batsman?" , "spread maximally" .)