Don’t know if the feeling is same for you but when I feel like im playing with the soft inner part of my lips is when I really notice the sound takes on character. Cant say Ive gained range but it feels easier to play and sounds better. I don’t so much think about corners (about 1000 different opinions about those) but try to concentrate on just letting whats in the cup vibrate freely. For what its worth, I have been working this or very similar approaches for 3 years always looking for more ease of play, this will hit you upside your head one day and then you will know. When its going perfect it feels like I make a cushion with the red part of the lip in what feels like a bit of a circle (its not) and the stuff you feel with your tongue when your mouth is shut is inside the cup doing the heavy vibrations. Some notes (high) tickle and my lips are really starting feel fine after 45 minutes of Clarke/. I was doing the oooh and when the mp hit the lip was changing before attack (don’t know what) but like yiu wasn’t getting the benefit, then I just placed it on the lip with the ooh shape with no chane then attack and immediately felt the difference, try to get a little more inner lip in there, there aren’t any muscles to resist air in that flesh. Youll know youre on the right track when lips tingle after a short passage. I know Im not Greg so take it for what it cost haha.
Rod