Armor bug?

Hi guys, how are you?

So, this is my first complaint regarding the armor,

I was studying the Tiger II (H) armor to be able to defend myself against the IS-2, but I came across this (I will explain it in the prints):

As you can see, the BR-471 ammunition can penetrate 205mm, in this case it could even pierce the Tiger 2 mantlet

But as you can see with the angled tiger, the hull has an effective thickness of 300mm~600mm depending on the angle, but the turret is also marked 300mm and even so, the IS-2 ammunition can penetrate.

My question is:

Is this a bug?

Best regards,

Gamoso

Analysis sometimes shows too big armor numbers, but color is not lying