I'd agree with that observation. A fuel hit will do you in when flying a P-47, and ack seems fine tuned to hit the fuel.
What happened to that whole "self-sealing" fuel tank thing?
A simple explanation would be that in most cases you've been hit, some hits actually did hit the fuel tanks, and yet failed to ignite due to the self-sealing tanks, or whatever method of modelling AH uses to depict its effect - thus, players only notice when the fuel ignites, and casually forget all the other instances when it didn't. Its entirely possible the "whole self-sealing fuel tank thing" is already working.
Ofcourse, unless HT chimes in there's no way of being sure.