I edited your post just a little but left the parts to possibly ponder on.
Something to try:
1.Take your finger and place in in front of your mouth about an inch away.
2.Blow a soft steady stream of air and without moving the tongue, make the feel of the air against your finger get faster. My guess is that you will manipulate the corners which will reduce the size of the aperture which will make the air feel faster against your finger.
3.Now do the same thing again but arch the tongue to make the air feel faster against the finger.
Hopefully we agree that in both cases, because the hole got smaller, the air got faster. It is not because the air got faster behind the hole.
The hypothesis I'm kicking around is:
Many of the ideas about speeding up the air with the tongue or compressing the air in the mouth by raising the tongue, etc. may not have a direct effect with playing in the upper register. These appear to be important tools we can feel or imagine. Methods that use the tongue to play in the upper register appears to be the result of tension being placed on the mandible to be pulled up which (when raised) puts the lips a little closer together which helps make the aperture a little smaller.
I've found very little that addresses this idea but when I read medical sites and texts on facial structure, there seems to be a anatomical reason for this phenomenon. A co-hypothesis? Is raising the tongue and it's effect on the mandible hard wired for suckling behavior.
Unfortunatley/fortunatley, that should raise the question " If the tongue raises and causes the mandible to go up which causes the bottom lip to apply force, what's the upper lip just below the nose doing when this is going on?"