The AA should flow with the battle, i.e. it should move with armor and not sit back cowering under a bridge near F (hint hint). One of the things i have noticed about the importance of F is that if my team owns A,B,C and D then the only possible path for the opposing team is to flank from the south, take F and use that as a spawn point to rush E/G and push D, which is an EXCELLENT strategy and one that is highly successful if my team ignores the signals. You have to play zone AS A TEAM and can't just sit at ABC expecting the other team to just ignore the other paths.
That said, I've often hounded my team to get some bodies south to hold the line between F and our side of the map so that we don't lose D or E/G. you need to be adaptive and reactive all at the same time. I find what usually happens is that my team will often fight with their blinders on and sit back playing ABC just because they have D and E/G, only to see the other team take F, move on the south flags and turn the tide of the battle and in the end, win. In the end, however, the AA still can't do it without the support of armor and should therefore stay with the tanks and APC's to provide air cover and vice versa.