Problems re international clashes with created cups

[Lloydey]

I have created a European super league complete with league and a cup with a group stage. I have avoided league games clashing with internationals by selecting "Domestic Lague - High" in fixture priority but one of the group stage games in the cup keeps being scheduled (and played) on an international date leaving most teams with youth and reserve players.

Is there any way to fix this? I don't see a fixture priority field in the editor for cups.

Thanks