Well, for starters you can see an airliner at that height, especially when (and this is important), it catches the sun, and that is the important thing about looking for the ISS, you need the sun over the horizon, it, against the dark back ground of the night sky, then the sun (which in your fantasy is hidden behind the atmolayer) illuminates it, and indeed a host of other satellites, and at the right time of year, noctilucent clouds too.