Brood over deal ultimately getting smaller (7)

I believe the answer is:

littler

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'smaller' is the definition.
(synonyms)

'brood over deal ultimately' is the wordplay.
'brood' becomes 'litter' (I've seen this before).
'over' means one lot of letters goes inside another.
'deal ultimately' becomes 'l' (I am not sure about this - if you are sure you should believe this answer much more).
'litter' enclosing 'l' is 'LITTLER'.

'getting' is the link.

Can you help me to learn more?

(Other definitions for littler that I've seen before include "Comparatively minor" , "Relatively small" .)

I've seen this clue in The Telegraph.

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