Conflict in Gulf then covering two leagues at greatest extent (4-6)

'conflict in' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?

'gulf then covering two leagues at greatest extent' is the wordplay.
I cannot really understand how this works, but
'gulf' could be 'g' (geographical abbreviation) and 'g' is present in the answer.
an anagram of 'then' is 'enth' which is located in the left over letters.
'leagues' could be 'll' (the abbreviation for league written twice) and 'll' is found within the answer.
The remaining letters 'ful' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?