This is just a simple carryover from single hand casting. Height = distance was drilled into me to keep me from staring at the spot on the water I was casting at. If you stare at the water you will throw your tip at the water and never hit that spot. Identify the spot you want to hit, then lift your eyes straight up to a target in the trees on the other side. On the Skagit, the best aim is at the top of the trees on the other side. Keep in mind this is in the context of the large bars guys like to fish from. Smaller streams and trying to get under branches will take some creativity.
What are my hands doing? Top hand guides and bottom hand provides power. I'm a lefty on the bottom and righty on top. When I pull the bottom hand it is usually coming towards the right breast/armpit area - but it kind of depends on how much clothing I'm wearing.
What usually causes my casting to slip is over powering. Thankfully after a long hiatus from spey casting,
@kerrys managed to spot this years ago and point it out to me. Of course, as soon as it was mentioned, it was obvious and brought back some of the things I'd learned over the years. One of which is to try and find the bare minimum of force required to cast the amount of line I was working with. A great exercise to keep you from "He-maning" your casts.