Against a narrow diamond, I’d make width a deliberate team advantage.
Your wingers should resist being pulled into every central duel. If they stay wide, the opposition full-backs have a difficult decision: step out and leave space inside, or stay narrow and allow the winger to receive.
The full-backs can still support, but they do not need to be the only players providing width.
Use the 8s to connect from central areas into the winger so the pass outside is not isolated.
I’d train against a compact diamond and reward switches that reach the winger facing forward.
The temptation is to match the opponent’s numbers centrally.
Sometimes the better answer is to use the space their shape has deliberately left.
At U17, players can understand that helping the midfield does not always mean standing nearer to it.
Holding width can help the central players by stretching the distance the opposition midfield has to cover.