Wondering if I should change my embouchure by pulling the corners of my mouth down in a mild frown. Having a bit of endurance trouble with pulling my mouth corners sort of straight (horizontally) in. In looking at pros while playing, e.g., Marsalis, many appear to be pulling the corners down. Some pros don't even look like they use any mouth corner moving muscles, e.g. Herb Alpert and Alison Balsom.
I welcome your comments and experiences.