For help figuring out exactly which System One PAP machine you are using, see my Newbie Guide for System One machines
As for your other questions:
Most people do see their AHI stabilize to a narrowish range that is consistently below 5.0. It may take several months to do so, however.
If your AHI is consistently running in the 5+ range night after night for several weeks, it's time to call the sleep doc's office back and let them know what's going on. An increase in pressure may
be warranted---if the bulk of the events the machine is recording are obstructive instead of central. And if you are actually asleep most of the time you are using the machine. (Wake breathing is sufficiently variable that it can cause the machine to score events that would not be scored on a PSG.)
And finally, you write:
Reader4211 wrote:I have slept with my machine 17 nights since I brought it home and I've averaged 9 hours per night 7 nights per week. My first concern is that my AHI numbers are bouncing around like a toddler in need of an unsweetened breakfast cereal. My lowest average for a single night has been 2.2. That was one of the best nights sleep that I've had in years.
People that I've spoken with who use CPAP machines have told me how those machines changed their lives so I had very high hopes when I brought mine home. I've had a taste of that greatness but only twice since I've been using the machine.
I know it sounds crass, but please consider yourself lucky to have had two "tastes of that greatness" in your first three weeks on the machine. Many of us go for months before we start to feel even a small smidgeon of that greatness. Many of us see very slow (but steady) progress in terms of our daytime functioning that can take 6-12 months (or more) before we can say that the machine really has changed our lives for the better.
So hold on to that sure knowledge that once you've mastered the art of sleeping with a six foot hose attached to your nose and having air blown down your throat, you will see many good nights in the future.