It's not a rear shot, It hits in the plate armor from the back side, but still a plate armor.
Kv2 shot make the same damage from that distance than from 100 mts away.
LOL, this game doesn't have that kind of sophisticated damaged calculation. There is only "Front" and "Rear" for any vehicle. There is no such thing as "side armor" even.
I'm surprised on how many people actually thing this game is even remotely realistic. Most RTS games including this one are closer to Pac Man than to reality.