Armor inconsistency

I was in a 12.0 match in an M1A1 and got penned on the turret side face by a BMPT APDS round. The game says it has 81mm of pennetration. The side of the abrams turret has over 300mm of armor protection, how does this make any sense if the round isnt either broken or defying physics


NERA protects mainly against chemical rounds (HEAT) and offers less armor value against kinetic rounds like APDS.