I know all AC blocks incoming physical damage. The + from AC blocks incoming magical damage. But what about AMF and GA, I don't remember.
For GA I see this in the wiki:
GA damage is reduced by AC due to enchantment, not base AC; GA damage type is GA.
Not sure what that means though, + affects GA? I get the second part.
For AMF I couldn't find anything like this in the wiki. It mentions RoBF lowering it; which I remember, but nothing else.