switch.dota posted this image. His estimate of the center of the aircraft is marked X. Note that he took MANY images, even made a movie.
That X... is also where the Nagumo force spawns.
Being spotted makes total sense, that's exactly how air encounters in SH4 work. If you are detected, you go from a small % chance of an airstrike being generated every X minutes, to a very large % chance of an airstrike every X minutes. Airgroups need not be attached to anything. Planes spawn out of thin air. There is no airbase near the X, however, just 3 CVs in the Midway mission (4 in any mods that fix it).
tater