Chatting to some folk today at the South Devon shoot, I get the strong impression that the real problem is not the toughness of the courses nor the break points for the grades, but the fact that there are too many people in AA grade nationally.
So if that is the real problem, address it in a way that will bring the desired result. If you want say 40 and no more in AA, then rank order the end of season scores and the top 40 go into AA. Share out the rest as you please; make each grade contain a third of the balance, perhaps.
Altering the "pass-mark" or toughening the courses will have an effect but it's not possible to predict with accuracy what that will be. Limiting the number who can have the coveted AA tag after their name fits the bill.