Mordred’s chest ain’t average sized at all. And, again, no she does not have an ass. There hasn’t been a single piece of art I’ve seen from apo that shows her with an ass of any kind.
I know there are pieces of art people like to cite as it showing she has an ass but don’t actually show her with an ass at all because people’s understanding of what having an ass is as non-existent as mordred’s ass itself.