Sorry you’re frustrated, I was there and may wind up there again but have gone from having a range of G above the staff to now working towards double G; high C is pretty easy and I can control it better than I expected. This is in large part to MTM and the aperture corners.
Don’t overthink things, there probably aren’t absolutes with what you are doing with your lips when playing, it’s more of a spectrum. You want to engage the corners and avoid clamping the middle of the top lip–what I was doing.
It helps me to close my eyes, relax and think about the ahhhooooohhh–feel the muscles in your face as you say aaahhhooohh with your eyes closed. Feel how your top lip middle part feels, probably relaxed, that’s what you want to do.
The Maggio Monkey and Clarke’s advice to tighten the lips towards the mouthpiece as you ascend help me, although that advice from Clarke is what I misunderstood when I first started playing. Now, thanks to Greg, I realize the tightening is supposed to be that of a tightening from around the outside of the aperture around it in a circle around the air column.
I try to stay relaxed, listen closely to my sound for maximum resonance and try to use as little movement as possible–kind of a less is more thing. It’s easier than we think, it’s more about coordination of our muscles and the air than it is about strength of our muscles or power of our air.
My $.02 / hope that helps. Good luck–the more frustrated you are now, the more incredible it will feel when you “get it”, which you will if you stay with it and keep thinking, listening / watching Grey’s videos and experimenting patiently. It’s only a matter of time.