Favourite bank is comparatively small (7)

I believe the answer is:

pettier

'comparatively small' is the definition.
('petty' can be a synonym of 'small')

'favourite bank' is the wordplay.
'favourite' becomes 'pet' (synonyms).
'bank' becomes 'tier' (both can mean a row of similar things).
'pet'+'tier'='PETTIER'

'is' is the link.

I've seen this clue in The Telegraph.

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