Not a bad idea in concept, but very few battlefields are large enough to make this meaningful unless you also reduce range on the smaller gun tanks. Even on a large field like SCAT the Shermans (and every body else for that matter) can reach you from anywhere on the field.

Another point is that, from my experience, most kills come at ranges under 20 feet. Those long range sniper shots are cool, but it is very hard to hit someone at 60 feet.