It has been suggested that the MmmmmAaahhhhOooohhhh is a fundamental portion of the WindWorks philosophy, and I totally agree. Our thought process on what are lips do when changing pitch is fundamental to our approach. Greg is trying to get us to consider, and possibly challenge, our current approach.
I think the portion that needs to change when doing MmmmmAaahhhhOooohhhh is going to be specific to each player, based on their current/normal/regular playing setup.
For ME, the most important part is the Oooohhh portion, and FOR ME, the key is getting the bottom lip forward, like the milk spout that Greg has talked about in a video in the Largo stage. But that is just for me – as I would historically have issues with my bottom lip collapsing and folding over the bottom teeth.
I do believe the bottom lip is like the facing of a reed instrument. It is what is reflecting the air to allow the sympathetic vibration of the lips. For some of you this is an area you need to address/improve, but others are already doing this just fine. This is why ultimately we are our own teacher.