I had the same issue for a while. Spent a lot of time blowing air through the leadpipe (i.e. no sound coming out) and experimenting to find at what point the vibration started and then taking pipe off mouthpiece to again find the point at which the vibration stopped when taking off the leadpipe. Trial and error * 100.

Agree with John that aperture corners important. I found when it all started to work as per Greg’s demonstration, my corners were slightly more inwards and the lower lip slightly more forwards. It felt very strange but very soon everything came together. You may find changes that work for you are very different I suspect. You are providing a structure with the corners where the lips want to vibrate and are not being forced to by a hurricane.

When moving through Ruby you will need to have the aperture corners controlled. This is possibly the biggest change for me. Not to diminish all the other teaching from M2M. Good luck.