More difficult in larger form (8)

I believe the answer is:

gnarlier

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'more difficult' is the definition.
Both the answer and definition are comparative adjectives.
Perhaps you can see a link between them that I can't see?

'in larger form' is the wordplay.
'form' indicates anagramming the letters.
'in'+'larger'='inlarger'
'inlarger' is an anagram of 'GNARLIER'.

Can you help me to learn more?

I've seen this clue in The Guardian.

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