Why can’t T57 in World of Tanks penetrate the bag on E5’s head?

The AP penetration of T57 can definitely penetrate the bag on E5. It's just the same as the bag on Fuxi 155's head. It's not that the cannons penetrate. You can tell by looking at the display on the AP bomb. The maximum penetration armor thickness is 336. But the bag on the E5's head doesn't seem to be made of paper, right?

263 is relatively simple. Leave aside the sides. Not to mention chrysanthemums. Almost anything with a penetration of 320 or above can be penetrated on the front. Especially the front face and the cheeks on both sides of the cannon. Everything is fine