Obviously I can't use the both at the same time (UC covers the mouth), and I decided to try the new mask first. When I put on the F20, I could feel it pushing my jaw back a little. That and some reading about neck flexion, cervical collars, etc, had me trying the soft cervical collar again. Here I am ready for sleep:
After 3h21m, I woke up feeling pretty uncomfortable due to the collar. Took everything off, put on the Ultimate Chinstrap, my DreamWear Gel Pillows mask, no collar this time, and slept another 3h until my alarm woke me for work.
Here's how the night looked in SH:
I can't really say much about how well the F20 and/or collar work for me based on this night because I changed them both at the same time and only wore them for 3h. The combination of the two doesn't seem great for me based on this one session. What I can say is that the F20 was pretty comfortable. It's probably my favorite full face mask (also own Simplus, Amara View).
The UC is very comfortable, soft, and seems to work really well for preventing mouth leak despite the fact that I can breathe through it if I try. I think the UC + Gel Pillows is likely to be my combination of choice going forwards.
Nothing I say on the forum should be taken as medical advice.