I'll offer my suggestion of reducing it to 3 for the first 2 difficulty levels, 2 for next 2 levels of difficulty, and 1 for highest difficulty. This way only way a solo player see's an AV is on highest difficulty.
My friend and I team on middle difficulty missions, but would want AV's. I think we can handle an AV on medium diff, but don't want to goto next level where the AV's difficulty is increased.