Sergeant major really in favour of cough sweet gets mint (5,7)

I believe the answer is:

small fortune

I'm a little stuck... Click here to teach me more about this clue!

'sergeant major really in favour' is the definition.
I can't judge whether this defines the answer.

'cough sweet gets mint' is the wordplay.
'cough sweet' becomes 'small' (I can't justify this - if you can you should believe this answer much more).
'gets' is a charade indicator (letters next to each other).
'mint' becomes 'fortune' (I've seen this in another clue).
'small'+'fortune'='SMALL FORTUNE'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for small fortune that I've seen before include "Large sum of money" , "But it's a large amount of money!" , "Lots of money" , "lot of money" .)

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