I am no expert but will add my observations. I am often accused of overthinking everything about my playing micro-scrutinizing every note. I love to do it and it is paying off. We more mature comeback players tend to take a more considered approach to playing.

Firstly the wet lips. I cannot play if I have not wet my lips. I do it without thinking every time I start playing. If you look closely I think that you will find that Greg does the same. If I am dehydrated I always find it difficult to play.

I have just experimented a little more with the lead pipe and withdrawing the mouthpiece. Typically I start with no buzz with the aahooh setup and when I withdraw I am still buzzing. Invariably the buzzed note is at a high pitch than the pitch with the lead pipe. Paul Mays (Prof of trumpet at Birmingham Conservatory, UK) attributes this to the fundamental note of the mouthpiece being high and to a release of air pressure from the lungs. He has shown that if he plays very high notes with the lead pipe that the pitch of mouthpiece buzz on withdrawal goes down towards the fundamental. Paul Mays actually recommends that there should always be a high pressure from the lungs when playing so when he withdraws on low notes the buzz goes very high. It is interesting that when I tried his way ages ago the pitch of my note went up in a similar way. However since I have been using the Greg approach the change is slight – it is still there. The Paul Mays approach seems to be to always maintain the core muscles in an engaged state – not so much kicking high notes but always having the air under pressure – he still recommends the ‘sighing’ approach to general playing.
All interesting stuff!!!
Best of luck
Colin