For this kind of thing, it would probably be better to add a bit to the card's rules text, after Covert. "This character may block parties that aren't Covert", or something similar. The flight mechanic you're talking about is identical to the Magic one, and Magic has plenty of examples where multiple evasion mechanics can be a real pain in the ass. I know when I build decks, I often tend not to take Flight into account - except defensively with spiders, but I do take into account things like Fear, Shadow, and the Landwalk abilities.
Never understimate the deflective powers of pumpernickel.