T1 Heavy armor goes from 101.6 to 46mm thick.
T14 armor goes from 101.6 to 50.8mm thick.
37 mm Automatic SH-37 will do 62mm of pen with premium rounds.
You've only played two heavies, both with rather weaker hulls. That 101.6 mm is the front of the turret. That's all you want to give the enemy to shoot at.
American heavies have gun depression. Hull down, hull down, hull down!!! If you do get a pesky light tank attacking you, try and back yourself against
an object. If they can't circle you, they're in trouble as your gun will be able to catch up to them. They don't want to be trading shots with you!
And if have nothing to back up against, at least turn your gun and chassis at the same time. I've had Cromwell's trying to 'circle of death' my TOG,
which has a fast turret and coupled with BIA and clutch-breaking, will surprise those thinking they'll out-run the gun.