Well, even though I am not a super model, all my female character are
Models, when they start out, do fashion shoots and such, but they don't know how they look in the shot cause they can't see what the photographer sees. However, eventually (raising in skill ranks Perform: modeling) they get an idea of what looks sexy and what doesn't.
Might sound a bit dorky as a comparison, but it works with hiding too. Eventually you get a feel for what makes good cover and hiding (rising in skill ranks) and you should have a fairly good idea if you can be seen or not. If given the time, I think you could take 20.