[JaM]

My opinion is that they get low becouse sometimes HEAT warheadhas problems to detonate properly, so penetrating plasma is not so strong.
"Weak point" is very good idea. There is not a tank that has solid protection over complete frontal arc. There are allways some spots whitch are weaker - mantlet,upper front turret, lower hull etc... Game dont have mechanism to simulate those parts of tank profile.So there is allways good chance to hit something that is not so good armored than rest of the turret or hull.