Thank you all for the thoughtful advice.
I have lowered the EPR, just last night, back to 1. Also tightened the range to 12-15, rather than the 4-20 I started with.
The other changes are headgear: using a Ruby chinstrap, and went back to the Swift nasal pillows.
For the night, still getting the red frownie for mask leaks, which were even larger and more frequent than before. Avg leak rate: 20.91 // 90% leak rate: 46.80 // Percent of time above leak threshold: 37.49%
At least twice the leaks lasted more than 20 minutes.
However, there were only 3 OAs: 10, 12, and 15 long.
25 hypopneas, all 10s.
10 RERAs but they all say (0)
12 Clear Airways, between 10 and 14.
AHI was 7.8, almost the highest since starting this machine.
Tonight will keep everything the same except use the old chinstrap which is the broad white elastic one that covers, and sometimes pinches, my ears. I've used that type for years, mostly because nothing else works. Even tried the boil and bite thingies, which didn't even get past the first 10 minutes.
If and when I get a Nuance mask, I'll also try it with both chinstraps, the Ruby adjustable and the big white elastic band.
Yes, it's likely that the chin strap is not effective as I had some dry mouth again, which had been absent for a while. As a former flutist, this is all so very strange for me to have breathing problems.