Don't fly so close to the enemy fields
ACK waits until you break a minimum range to the field before it starts shooting (say 1 miles) but once it starts shooting at you, it will continue to shoot until you are much further away (say 4 miles).
Also, once you have become a target for ACK it will continue to target you even if you break the (4 mile) barrier and come back. (e.g. it doesn't wait until you break the (1 mile) barrier again before it shoots at you again) - You are a target for the entire flight, until you .ef.
88mm and 5" flack sucks, just deal with it the hard way. As much as I hate the garbage, it's a necessary evil in AH.
That being said, it would be nice if it acted more like real ACK.