There's a reason why 3.4gr is a starting load, and you found out why. 4.0 sounds like a fine mid load, go for it.
BTW AA2 really isn't known for 9mm. Try 231, Universal, Bullseye etc.
I've seen AA#2 start loads as high as 4.4 .... and even that fills less than 1/2 the case.
I'd find a more suitable powder. Low load densities don't make for consistant loads, and leave room for a double charge.