Most of the front of the turret is invulnerable to anything in AH. It has the mantlet and the turret front armour.
Over 200 mm of the best quality armour steel in WW2.
I see a lot of people try to add the armor of the front of the turret to the mantlet . . . I think that is a mistake on most tanks. Below is a pic of a turret mantlet removed from the turret. Note the gun, sighting equipment, etc. attached to the mantlet.
Now here is a pic of the turret without the mantlet.
So the mantlet essentially covers a huge, gaping hole in the front of the tank, meaning except for the small area where they overlap, the armor of the mantlet and the turret front aren't additive.
I can't find a picture of the Tiger specifically -- at least not a real one, just lots of models, and I don't want to assume those are put together the same way as the real deal -- so the "hole" in the front of the turret may be small relative to the whole mantlet. But if it is similar to the pics above, the likelihood of having nothing behind the mantlet may be much greater than having some additional armor. If anyone has additional information, especially decent pictures, I'd love to see them.