It's a lot more complex than this, if they remove shells crashing into the ground, then what happens? Shells will just fade into the underworld and disappear when they miss, and most AI Tanks which rely on shells hitting the ground to kill nearby infantry will suddenly become useless. The only alternative I can think of would be to make tank shells arch a bit to try and get over 'bumps', or alter how accuracy + target size functions so that guaranteed hits roll much more often.
Target size of an armoured unit should judge the height at which its projectile is being launched, where increased height advantage (i.e. King Tiger) means less of a chance of that unit's shell's hitting a small bump or hill in front of them.
This would promote smaller armoured units or light vehicles to have to utilize their mobility to get on the higher ground, where heavier armoured units will still have a fighting chance battling up hill, at a slight penalty depending on target size