Hi Rod, thanks for your email and pleased it is helping.
The sensation people have varies SO much that there is no right or wrong, it is so individual.
My sensation when playing in the upper register is like a tickle going across the middle of the lower lip. There is no feeling of back up or choking because it takes a lot less flow of air to play than what people think.
I can feel where my tongue is at, what my aperture corners are doing and how much air is required at different volumes. There are a lot more videos coming to explain this further.
All the best,