Jail sentence still active after death — that's disproportionate (6-4-4)

'disproportionate' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?

'jail sentence still active after death' is the wordplay.
I cannot quite understand how this works, but
'sentence' could be 'life' (life sentence in prison) and 'life' is located in the answer.
'active' could be 'a' (grammatical abbreviation) and 'a' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

'that's' is the link.

Can you help me to learn more?