Why are you not zoomed in consistently? I just did this off line with the Firefly, T34/76, Panzer, Tiger, and M-8. From the same spot, zoomed all the way in, it was dead on for all, AP, HVAC, or HE. Even Smoke in the Panzer.
I can post screen shots also, if you like. I used a AA gun for reference, lining up the range line on the top of the gun shield. Same range line for all tanks and hit the same place on the turret each time.
Maybe it's just you?
wrongway