Thanks Pat for your thoughts I will consider them further.
Since I wrote the original post I have had time to question my own thinking further. I went through the Largo videos again and found connection with the Largo Upper Register Development videos and the related upper register development videos in the other levels. What struck me as important in these videos was the easy responsive buzz of Greg’s lips to the airflow. I found mimicking this difficult to do initially but then it came very responsive. This I believe was the result of the space between the teeth being wider and the lips losing their stiffness.
So now even the slight airflow causes the lips to vibrate when lightly placing the finger tips on the aperture corners. I also obtained that octave jump spoken about when the finger, rim and mouthpiece are place on or taken off the lips. I believe I have had started to maximise the sympathetic oscillation. Just in general playing this approach has opened the sound and I am achieving greater flexibility. I am hopeful this approach, particularly reducing lip stiffness, will allow the aperture corners to form and move more easily and the jaw will as a consequence relax. More experimentation and practice to come.