Tried the chin strap with the nasal mask (the one that uses air pressure to make the seal. Never could get it right, and with my sinus issues, sometimes end up breathing through my mouth anyway... You're right: the pressure-driven open mouth dryness is unbelievable. I felt like if I held my breath with my mouth open, the air ran in my nose, turned around and went right back out my mouth.
Like I described, I kicked up the low pressure on the ramp by a few cm and shortened the ramp time way up. And at that, I often just start on full.
It's also pretty crazy - I had felt for weeks that the pressure was too low, even had it calibrated at the place I got it (was like 0.1 cm low). When I figured out how to kick it up just 1/2 cm, I actually slept better...and that experiment was a whole lot cheaper than another study! I may try a little more experimentation...
I use an Ultra Mirage also and am pretty happy with it. Awkward to travel with the whole mess, but I've got it pretty much down now. The one trip where I forgot the power adapter was kinda uncomfortable, though.
RFTraveler