Stout poles properly set are most thin on the ground (8)

'most thin on the ground' is the definition.
I can't judge whether this defines the answer.

'stout poles properly set' is the wordplay.
I cannot really understand how this works, but
'poles' could be 'spars' (spar is a kind of pole) and 'spars' is present in the answer.
an anagram of 'set' is 'est' which is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

'are' acts as a link.

Can you help me to learn more?