Runaway pressure due to wrong mask setting on S7? AutoSet

Just debugged a problem that may be of help to others. I have an old ResMed Autoset Spirit from 2007 (an S7 maybe), was using an old Mirage FFM, which the machine has a mask setting for. I'm on Autoset 8mm - 14mm (still experimenting), with 95% pressure ranging from 9 - 11mm the last couple weeks.

3 nights ago: received a new Quattro FFM, switched to it. In the morning, saw 0.0 leak, implying that the vent rate of the Quattro + actual leak is less than the Mirage FFM's vent rate. Usual pressure (11) AHI (1.2).

2 nights ago: wanted to be able to see some variation in leak data, so I changed the mask setting to "Normal" and looked up in the device manual what the vent rate for that was, to compare it to the Quattro vent rate. Had a horrible night, trouble going to sleep (prob bc I changed my sleep meds), and then aerophagia and vague discomfort all night and many awakenings. In the morning, was surprised to see my highest ever 95% pressure of 14 (my max was either 14 or 15), with the usual (for this week) low AHI (0.9). Thought the pressure was just an anomaly ("maybe my airway was really blocked last night and needed a lot of pressure"), until...

last night: Had the same discomfort with the cpap pressure, strong chipmunk cheeks even under my FFM, feeling that air was being forced into my mouth, and aerophagia. Halfway through the night, I woke up and sorted through the data in my mind "WTF changed? I bumped min pressure up from 8.4 to 8.6, but that wouldn't do it. I got a new mask but that was the night before. I bumped max pressure up to 16 because I hit the max the prev night, but why would the machine be reaching it? The only thing I changed the night that this started was the mask setting. Hey, wait a sec, that could affect the autoset...". So I changed the mask setting back to Mirage Full, and had a good second half of the night. I don't have full-night data so I can't verify that the pressure was lower (95% was already pegged at 16mm by the 2nd half of the night), but it sure felt better.

I don't know how the mask setting affects the autoset - perhaps putting in a mask with a lower vent rate makes the machine think the mask is leaking when it isn't, and bump up pressure - but it certainly seems to.

My S9 Autoset is marked by USPS for delivery today, woo-hoo! It will have a setting for the Quattro, I'm sure. I'm also going to lower my max pressure perhaps to 12, for now I don't seem to be able to tolerate higher pressures.

Bump--so somebody smarter than me can help!