Recently started CPAP -- very high proportion of Clear Airway Events

[matt2]

Hi all! I just finished night #19 of CPAP therapy. My headaches, grogginess, and general tiredness have definitely gone down since starting, but I'd still like to optimize my therapy as much as possible.

My specs:
- Resmed Airsense 11 autoset
- Pressure: 6-18 cm H2O
- Mask: just switched to Airfit P10 Nasal Pillows, was using F&P nasal mask for 17 nights
- Tubing: just switched to ClimateLine heated tubing, was using original tubing for 17 nights
- Sleep study diagnosed with 39.9AHI

What's going on:
- My best night so far had a AHI of 3.35 (that was the best morning I had in many many months)
- I average an AHI of 8.91 (1.03 OA + 7.19 CA)
- I still remember waking up multiple times per night (usually at least 2-3 times) 
- On occasion I wake up with dry mouth (like 50% of the time)
- I'm still awaiting a follow-up sleep study with the CPAP, and have been instructed to not change my pressure settings

My questions:

1. I'd like to get my CA values down. It seems the majority of my AHI comes from Clear Airway events, what can I do to reduce this value? I've read that CA events are usually higher when starting therapy as your body needs time to adjust. These values still seem high so I'm trying to figure out ways to bring it down. It's the proportion of CA to OA events that are a little concerning to me... what's a normal range like?
   
   
2. I'm trying to decide between mouth tape, a chin strap, and a soft cervical collar.
   I wake up with dry mouth pretty often. I'm guessing it's from mouth breathing, but I haven't experimented much with my humidity settings yet. And I find that I get pretty bloated from swallowing air in my sleep. I was considering getting mouth tape or a chin strap, but then I learned about soft cervical collars. What should I try first? I think cervical collars are more for keeping your airway open (eg. stop chin tucking). But my OA values are relatively low compared to my CA values. So could I still benefit from cervical collars?
   
   
3. Can positional apnea lead to CA events?
   Before starting CPAP, I noticed my snoring and apnea was much worse when I was laying on my back. I usually start my night on my stomach or side, but I toss and turn a LOT in my sleep. Sometimes I wake up on my back. I understand that sleep position and chin tucking can affect obstructive apnea. Can it still lead to these Central Airway events?
   
   
4. How is a "clear airway" defined? I understand that OSCAR displays data from the CPAP machine. I also notice that my airsense 11 displays an obstructive and central sleep apnea value. Is the "clear airway" stat something that is defined from the machine?
   

OSCAR data
Some pretty lines and numbers from OSCAR 

My best night (AHI 3.35) -- was still using an F&P nasal mask this night
   

My last night (AHI 11.18) -- second night with P10 nasal pillows