Actually, maybe there's a bug with the thickness calculations, or maybe not. I would test it, but I don't have the time atm. - but you can do it yourself:
1) Look for A) a tank with heavy front, and notedly thinner side armour, and B) some AT-weapon which can only barely (With luck) penetrate the front or the strongly angled side armour
2) Set up a battle with those units in the battle editor. Don't forget to set both sides to human. Remove all ammo from the tank, so it can't shoot back automatically.
3) Save !!
4) start the battle, and fire away. reposition the tank every round to test various angles, and reactions which occour then.
NOTE DOWN EVERY MESSAGE 'bout weapons fired, missile hit and penetration (values) achieved.
If it goes boom, just reload the battle ... . Do that several times until you've fired 40-50 shots, then come back and report the resulting statistics...
