On Noriko's butt rating system, Maya is apparently the best:For comparison, Ami is an 8/10:And apparently according to the/a(?) Italic Narrator, Sensei rates Nodoka's as a 9/10:So, I'm assuming Maya is likely a 10/10 based off the current opinions that have been given within game, and assuming Sel wrote all of this, it seems like it's intentional. (Albeit, I can definitely see Kaori beating Maya in Sel's pov considering the context)
Also there is more to Butts than Size. So uncultered (kidding).. Honestly I have no idea how to judge it. I think it's kind of how Molly described "Moe". It's something "you can feel inside of your bones". I was also mostly kidding about the Maya thing, but(t) I would be interested in the in game explanation though.