Okey dokey, I’ll try, but I’m bad at explaining things.
First of all, it’s hard to tell because Kirby is constantly bouncing, but I’m fairly certain he is slightly taller than Meta Knight in Smash 4.
Second of all, I think the cape was designed to accommodate someone with wings. The inside of it is likely a pocket dimension of some sort, which would explain Meta’s ability to disappear by pulling it over himself, and it explains how his wings are completely hidden. Anyway, it hides Meta Knight’s wings, but it can also transform into them when needed. This is a bit confusing, since that would make it both part of his body and not, at the same time, right? Nah. I think it’s like putting a blanket over your hand. You put it over it and you can’t see it anymore (I mean, you can probably see where your hand is because of a lump, but ignore that. Your hand is invisible now). But, if you were to grab something with the blanket still covering your hand, would that make the blanket your hand now? Nah, it’s still a blanket, it’s just covering your hand. Anyway, I guess that’s the whole deal with Meta Knight’s cape, when it transforms into wings, what you’re looking at is the cape, but the wings are underneath/inside it? If that made any sense. I have no idea, it’s 3:52 in the morning and my brain is functioning on another plane of reality, so… yeah.