If this also applies to AT guns they might become pretty useless. They already miss quite a bit of shots at near max range, and if they receive less penetration at long ranges chances are that they don't penetrate even if they manage to hit.
It should be reasonable to expect different AT weapons receiving different penetration modifiers at different ranges. AT guns could retain high penetration throughout while T34s could get more falloff further away and ramp up faster when closing the distance, for example.