I'm sorry, but this is hilarious. Flanking is not rewarded? Most of the tanks have half the rear armor compared to their frontal armor, so you have almost always a 100% chance to penetrate. There are a few exceptions in both directions.
The heavy assault guns / tank destroyers tend to have far more frontal armor compared to their rear armor, examples would be:
Jagdtiger: 525 front, 150 rear (29%)
Panther: 290 / 110 (38%)
Elefant: 400 / 150 (38%)
...
There are like I said also exceptions in the other direction, units that have more than 50% of their frontal armor as rear armor. Those ones are they heavy tanks:
King Tiger: 425 / 225 (53%)
Tiger: 300 / 180 (60%)
IS-2: 375 / 205 (55)
Why is that? Because these tanks are extremely slow and easy to flank, but also need to be directly in the center of the action. The support guns listed previously need to stay at range and their armor reinforces that role - flanking is super efficient vs those since it's hard to do and creates an interesting gameplay where a player needs to protect those. Flanking against something like a Tiger on the other hand is far easier to do - it can't stay on range and it is not really mobile (less mobile than IS-2 unless it's blitzing, FYI). So I'm fine with the concept and I honestly don't think that rear armor would change that much. If you fight a heavy tank and you can flank in most cases you drive right behind him to block his escape route. Even with side+rear armor that would make those tanks too susceptible to flanks and too punishing, so the design in the end would stay similar I guess.
It's called rearing, there's no flanking in COH