I like this. What do you think?
The type of gun become less effective above a certain altitude, but can reach higher than the limit on MP-4. (Reality adapted and somewhat reflected into playable game form.)
Light: Both light and medium guns can fire at you when you are higher.
Medium: Light and Medium Guns can fire at you when you are at a lower altitude and also heavy guns when you are higher.
Heavy: Medium guns at lower altitudes and only heavy when you get higher.
Almost every source tell us that flak was very effective at the altitude the medium and light bombers flew on. I could change the medium values to heavy and the heavy to medium to probably reflect that opinion better, but then this game would become too deadly...
But then again, with the Evasive Action on The Bomb Run option, it could work. The Medium and light bomber formations frequently applied that tactic to avoid flak.