Thanks John. I totally get that Shape changes pitch. However my question was really about how our body should feel with regards air pressure / compression when ascending playing at a level volume. ie Results driven. So either playing a scale or slurring from low to high. I feel that from low C to middle C only a slight increase in air compression. From middle C to D not much change. Then as I approach E (top space) there is a bigger increase and a real gear change for top of the staff G. Of cause what I feel as a relative beginner will feel a lot more significant than for an established player who I presume has got used to air compression in the body. This air compression is certainly not linear.

Gregs video on the Slingshot demonstrates this (I think) where he says he sets pitch and volume before releasing the air by dropping the tongue. A results driven exercise. As he plays a higher pitch he seems to compress the air with abdominal support.

I suppose I am trying to ascertain whether I am trying to hard or its just a feeling that I am not used to. Note there is no pinching of the lips or closing of the throat. Generally I feel relaxed.