John your post makes perfect sense to me. I too have noticed that when I get everything right I get that magic moment when the notes just fly with such ease. However as yet I haven’t found consistency. I have also discovered how little the aperture corner movement is to change pitch the further you ascend. That and building my embouchure muscles mean that focusing on middle C upwards is useful for me. My favourite overtone series at the moment is Eb. When I get that right I hit Ab above the staff. The funny thing is I know when I am going to make high Ab by the feel of the airstream and lip vibration as I slur through middle C to Eb using some air support. I am going to focus on doing more passive air exercises to see if I can improve the aperture corner feel. My range has certainly improved over the last couple of months in that the higher notes are getting easier and notes above the staff are starting to speak. I just need to be patient. Thanks for your posts always helpful.