Hitech,
Does the box grow when maneuvering as well?
Also, are the shells actually "fired" and have to travel to the hit box, or is the hitbox basically where the shells "land?"
If it's where the shells "land," like I'm imagining, I'm wondering if maneuvering doesn't seem to help avoid getting hit since you aren't maneuvering away from the shell is being fired.
In other words, if the hit box where to lag behind the aircraft's acceleration in any given direction, it could emulate the time it takes a shell to travel from the muzzle to the aircraft since you can't steer the shell once it's been fired. This way, the box would stay more concentrated on big lumbering targets, but would have a harder time tracking the smaller and more nimble ones, particularly in radical direction changes, like in dogfights.