According to the textbook I'm studying, antenna design (and reflections I guess) often cause energy to be radiated in multiple beams and you can get GS indication on one of the unintended beams. The antenna design ensures that the lowest beam is the correct one. Therefore, if you enter from below you can be sure of capturing the correct GS. If you enter from above, you may capture a phantom GS.Hopefully the textbook is telling the truth!Nick.