I have severe apnea (~40 AHI untreated). I didn't get much better than 20 on APAP, until I changed several settings with help from this forum.
In short, my treatment wasn't working because (1) the settings on my APAP were too wide (4-20), and (2) this caused the APAP to run very high so I kept losing the seal and couldn't tolerate the exhalation pressure. EPR was set on 1. With the settings on 4-20, my 95% was around 18, which I couldn't tolerate.
Based on suggestions I read on this forum, I reduced the range (8-16) and set the EPR to 3. Now my AHI is under 5, and my 95% is around 12. For whatever reason, having the range set from 4-20 prevented the machine from working correctly at all, but it works fine on the narrow range, and I can exhale with the EPR setting raised.
Can't thank you all enough. It's been a long, tiring road.