I wear my mask right below my mouth. After a few episodes of waking up to swollowing air , I moved it under my lips. That somehow worked and I keep my mouth shut. I do not have a chin strap , and I use the AirFit F20 full face mask. No nasal pillow mask. I have been sleeping very well , have been using about 3 weeks.
I purchased a CPAP pillow and have been using it for a week. I have been on CPAP for less than a month , and the pillow did the trick for me ! I am a side sleeper , and my mask was irrating my nose to the point that I developed a bump on my nose , I wear the full mask because it helps stop me from mouth breathing. I did switch styles a bit more flexible around the face , that helped , but the pillow did the trick ! I highly reccomend it.