if you look closely you can see that kcm creates the yellow chackra around your clothes thats why minatos kcm has a cape coz he has it.....narutos kcm is his clothes and bm creates a special coat......
Minato cant have bm even if he has half the kyuubis chakra because Naruto has the actual Kyubbi inside him so he can have more power if you know what I mean