The glide is actually one of the versatile jump types. The thing is the actual glide phase moves you in the direction and speed that you're going when you hit x the second time. If you hit it too late and you're already past the apex of your initial jump all it will do is maintain you slow downward momentum. it you hit it just before the apex you will continue upwards at the speed you were moving at that point, with reasonable directional control. If you quickly double tap you basically jump and glide at the same time, hurling you up at high speed. Where the glide realy shines is that if you hit x a third time you cancel it and drop straight down basically on command. People say warlocks hover too much and are sitting ducks, but a skilled glide user can surge up into the air and drop out of the sky erratically and unpredictable, making thm hard to get a bead on.