Dwindles when Allen's away (6,3)

I believe the answer is:

peters out

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'dwindles' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'allen's away' is the wordplay.
'allen's' becomes 'peters' (I can't justify this - if you can you should believe this answer much more).
'away' becomes 'out' (synonyms).
'peters'+'out'='PETERS OUT'

'when' acts as a link.

Can you help me to learn more?

(Another definition for peters out that I've seen is " comes to nothing".)

I've seen this clue in the Sydney Morning Herald.

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