Really can fit when adjusted properly (2,4)

I believe the answer is:

in fact

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'really' is the definition.
(synonyms)

'can fit when adjusted properly' is the wordplay.
'can fit' can be anagrammed to 'IN FACT'.
Though, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for in fact that I've seen before include "'In reality (2,4)'" , "really!" , "Actually" .)

I've seen this clue in The Globe and Mail.

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