I think if we could see hit % of puffy ack, it would be extremely low, but with dozens of shells going off in the air around you, eventually you will be hit.....
That said, as much as we need puffy ack in the game, it's AI engine should be tuned such that it preffers to shoot at multi-engine bombers.
I think the "simple" solution would be to change it so that it does not fire at aircraft unless they fly straight and level for more than 10 seconds at a time.
On a realism scale, how often would a real WWII gunner crew fire at a small, high-speed aircraft at great distance that was constantly maneuvering and changing altitude?