I thought byul used to have a larger frame or is that my imagination?

It's because when he's with Siwoo, he looks way smaller. Byul really have a smaller frame since he hasn't developed that Alpha shish thing that Dojin was talking about

So when byul starts to be in-love-love then he'll grow muscles too, and they'll be a muscular alpha pair in theory? But I doubt that would happen since idt the author made that type of pair before but who knowss -w-