I should have asked you earlier, but what are your AHI numbers like? With the Essentials turned to Plus, you should be able to see an average of all the data you have collected to date with a breakdown of the obstructive, hypopnea, and central apnea events. You can set the time interval that the data is averaged over.
I also have an AutoSet machine and have it set for a fixed pressure, which in my case is 11 cm. I have issues with central apnea and have found that if I use a fixed set pressure the machine does not get carried away and increase the pressure too much and cause even more CA events.
I do have my machine set up a little different though. The AirSense has more features than the S9 (which is the machine my wife still uses). One is the AutoRamp feature. I use it and like it. It monitors your sleep and ends the ramp automatically when it decides you are asleep (to a maximum of 30 minutes). It is not really a ramp as it just maintains the pressure at a fixed value that you set with the Ramp Start pressure. I find 5 cm is much too low for me as a ramp pressure, and I currently have mine set at 9 cm. I like to be able to breathe deeply without feeling that air flow is restricted.
The other thing I do is set the EPR to 3 cm, and further set it to Ramp Only. This way during the ramp I get 9 cm on inhale, and 6 cm on exhale. I find that more comfortable when I am going to sleep. When it decides I am asleep it switches to a fixed 11 cm, and stops the EPR, so inhale and exhale pressure are both at 11 cm. The benefit to that is that it can reduce obstructive apnea events which can start during the exhale phase of each breath. It allows for a lower set pressure which is more comfortable and at least for me avoids some of the central apnea events.
I hope that helps some. If you have any questions just ask. This is an example of what you can see with OSCAR. I am still using the previous version called SleepyHead, but it is very similar to OSCAR.
I have used the P10 mask pretty much from day 1. I did try a F&P Brevida but did not like it as much, but my wife did, so she now uses the Brevida. I also tried the Swift FX nasal pillow mask, but I could not tolerate the high velocity air exit from those holes in the mask. It kept waking me up during the night. My issue with the P10 is not the mesh vent, as I love that part of it. I find it amazingly quiet and no high velocity air. What I dislike about the P10 are the flimsy straps. Tried various things, and then finally decided to make a hybrid mask which is the P10 modified to accept the Swift FX headgear. That is what I use now. Here is a link to a post where I described how I made it.
I am not sure what to think of the CO2 being a problem. These masks are all designed for a certain vent flow that is to keep the CO2 in control. In general the larger the volume of the mask, the higher the purge air flow.
This is a clip of the technical specs for air flow on the Swift FX. At 10 cm pressure it looks like the air flow is pretty close to 32 L/min. The volume of the mask is 103 ml.
And here is the P10 mask. I see the air flow is almost identical, but the volume of the mask is a bit larger at 123 ml. So yes in theory on a relative basis to the volume the FX has a higher flow.
These specs can be found in the user manual. For my purposes in reducing central apnea, the lower purge rate, and higher CO2 may be helpful to me.
