I noticed your post a few days ago and was waiting (and hoping) for someone with more experience in the course than I to respond.
Since that has not happened I am happy to give you my opinion on the matter, for what it is worth. I am not a pro player, nor am I a teacher or academic who has had a lot of exposure to great teachers or professional musicians, but I have played for many years and have had about 6 months experience in this course.
I believe there is not one right position of the jaw or teeth. Since all humans are a little different I think we served better by focusing on sensations/feelings and results.
For example, I am a downstream player with a slightly receded jaw when playing. When working on the Windworks exercises, I have been working on bringing my lower jaw more forward while also striving to keep my throat more open. I then monitor my sound when not doing pure process exercises and adjust and experiment to see what produces the best sound. Completing the course exercises, using what I will call this Windworks setup, combined with trying not to overblow and over engage the core, has brought me better results in my old set up with the Windworks setup still not feeling secure enough to use when playing.
With all that said, I would answer your inquiry by saying that perhaps you should not focus on the teeth position, but focus on an open throat and reduced core engagement. This may keep you more relaxed and therefore lower the tendency to close your jaw. As Greg would say, keep the foyer and body’s concert open and resonant. I find if I focus on openness, my aperture corners, and the resonance of the sound I am creating, that my jaw naturally moves to where it should be. The jaw opens slightly for lower notes and closes up slightly for higher notes as the corners of the aperture tighten. I do not think specifically about the gap between my teeth when playing and this seems to be working for me.
I hope you find my comments helpful and wish you success with the course.