When you hook someone they travel fixed distance to you, if you hook someone in mid air, they are not going to land on their feet. They are going to land somewhat above you, depending on how they were dragged. If you hook someone who was standing above you on the ledge - they are going to end up being slightly above ground and slightly outside of range of your scrap gun LMB. If something was between you and your target - same shit, they'll end up being further away from you than usual (because their drag distance is exactly the same, but drag "path" is longer).
But i did noticed some wonky shit like Pharah being able to use her thrusters to jump up while being dragged, she kinda "froze" in the air for the duration of a drag with blue flames behind her back, so i just RMB her to death.
I think i'll check these situations in custom lobby with my wife when we'll get off the work today.
Basically, from my observation, hook drags your target a fixed distance all the time (depending on how far away your target was when hook connects), so extra distance between you and target (via obstacles than target has to be dragged over, or extra dimension axis) will screw you up