I always think the comics stray into treacherous waters when they try to use cod-science to explain the seemingly magical nature of Superman. The notion that he flies by vibrating air around his body has always seemed weak, so too any attempt to explain why his cape doesn't make his shirt look bulky. Just leave it be: it is what it is, and we can accept the inexplicable if it helps in the creation of enjoyable fiction.
It reminds me of all the laboured efforts to remedy the Daleks inability to maneuver over stairs. How about we just don't show situations where they have to go up stairs?