Two changes relative to fields and the like, that I would like to see considered.....
Bunkers... Having had to work in and around ordnance bunkers, I will tell you plainly that they are completely immune to gunfire. Several feet of reinforced concrete requires specialty-fuzed bombs to penetrate these things. Near-misses do nothing whatsoever. Direct hits with instantaneous fuzes will do little to nothing.
Vehicle resupply... Nothing is more frustrating than to knock out a turret only to have it repaired in a blink of an eye. Supplies should just resupply, not instantly repair. Have a gun knocked out? Return to the spawn or hanger and get a new one. Tracked? Should require a period of time to repair, but only if not within machine gun range of the enemy (a crew will not attempt to repair a track under fire). Maybe we need recovery vehicles....
Other things... 88mm guns traverse far slower than I've seen in films of actual guns in action, especially if the gun crew pushes the gun around on its mount. I suspect the 17 Pounder would traverse faster as well.