I think you will understand it better, if you Google up ILS localizer (or glide slope), and look at the pictures. Let’s speak about localizer for instance, and forget glide slope for a minute, as it wouldn’t exist at all. Your LOC instrument senses two vertical beams, one means “too much left, go right”, the other one the opposite. The two beams each have to be oriented vertically, otherwise (if they would be oriented horizontally), your LOC instrument wouldn’t see them if you would be anywhere “above”, or “below” the localizer beam. So if you are off to the right (regardless of your altitude !), your antenna gets the right side beam’s (vertical shape) signal stronger, which moves your LOC bar to the left. Now if you go left, you start drifting back into the left side beam (which is also vertically oriented, so that your instrument can pick it up in any altitude), that tells you “you are left, go right”. Flying in the middle, the two beams are like two equally strong springs, that are each trying to pull the needle to themselves, so in the middle the two beams have equal effect on the needle, so it stays in the middle. But the “left” and “right” beams themselves, each has to project it’s own signal vertically. Hope this helps, sorry, if a bit confusing.