Thank you John for another very full response.
It is all making good sense.
I have been concentrating on separating air from the pitch and it is slowly sinking into my rather old brain. Clearly differentiating between passive and active air and the smooth transition between the two is starting to work.
However, my articulation from the top of the stave is not very good at the moment. If I do a simple arpeggio F, A, C to F (top line) and slur the top F is spot on in tune. But if I tongue the top F goes sharp – really irritating.
Your advice on concentrating on shape is working although I still revert to the old way.