Rear armor being half of the front armor is the most common case, but its only true in maybe 50% of the cases.
Might contain some unused squads for multiplayer, didn't filter.
Actually, I think elchino7 means the percentage of the unit's model/hitbox of which the frontal armour and rear armour applies.
I've heard the claim the Panther's rear armour is just 20% of the hitbox a few times, never thought much of it.