I'm not sure if I've explained my idea 100%, so I'm open to any feedback.

It may sound funny because in a porn site you'll expect most of (adult) women being draw with big breasts and ass. But depending of how the artist do their work the asses they draw are not entirely big, just average or just with a nice shape. This could make people debate whether their favorite works should have this tag, yet you'll see "small breasts" tag on some lolicon works. I mean it's implied they don't have big breasts because if you wanted to, you could simply search oppai-loli.