I have a question for the OPer. If you were standing anywhere near the pentagon and a plane flew at over 500 mph at a low altitude, how easily do you think you could place where the plane is/was ? Unless you knew that is was coming and from where, there is no way you could get a good idea of where it is/was.
But if I was standing at the citgo gas station, looking, say, north, I would probably be able to tell if the airplane was in front of me (in my sight) or behind me (not in my sight).
Again, this doesn't mean that the eyewitnesses who think the plane passed north of the citgo station are correct... It was hectic and eyewitnesses can be unreliable.