The fae mien superimposes itself over the mortal seeming while within a freehold. Same thing for the Dreaming. Changelings see both at once, unless someone's hiding behind their mortal seeming, Which side they're paying attention to depends on what's going on -- if someone pulls a mundane gun on you, you'll be paying attention to that, and also paying attention to your attacker's chimeric wings which can give you a concussion if they connect.