Bad titration study?

I have been on CPAP since Feb of this year and my sleep doc told me my pressure were 20/17 and I was prescribed a non automatic S9. However, the main problem I had been having was constant mask leaks and I have tried several kinds (nasal, pillows, hybrid). My wife even got to the point where she would end up in the guest room due to the leak noises (mask farts) not to mention my constant waking up to refit the mask. My sister has been on CPAP for several years and asked me if I had tried a lower pressure. I had not.

Therefore, I decided to try an experiment. Lower the pressure setting on my machine and see what happens with the graphs. About a week and a half ago I set my machine to 15/12 to see what happens with the intention of raising the pressure back up if the numbers were horrible. The numbers are better than ever with AHI below 1 every night at the new settings and I get more sleep because the leaks have become minimal.

So what happened? Did the tech screw up? What could the doctor see in the sleep study graphs to cause her to agree with the pressure settings? I'm due a follow up visit next month so I will ask her some pointed questions.

I do not have years of medical training so I am hesitant to question the doctor's expertise. I know I do not like it when amateurs question my expertise in my field. I'm just confused as to why the lower pressures seem to work better than the prescribed settings.

I would ask the doctor any and all questions you have without hesitation.

That said, I don't think it's unusual that once you started using the prescribed pressure that you found it too high for you. I had the same situation and found out very quickly that I needed to lower the pressure, and had good results by doing so.

Doctors prescribe what they think will work, but you ultimately decide what pressure works best for you.

One night in a foreign sleep environment doesn't automatically equal what we have at home night after night.

Wonder if sleep position plays any part in things? Like sleeping on your back? Perhaps more supine sleeping at the titration study (they encourage this because often supine sleeping will be the worst case scenario) and maybe at home you don't sleep on your back that much. Don't know if that would pertain to you or not but it wouldn't be unheard of.

Maybe at the sleep study you just had a really bad night and happened to catch it and needed a bit more pressure??? Who knows but one night in a foreign sleep setting doesn't always mimic what we have at home. Be thankful you can do well with less pressure than originally advised. In my case....I needed more pressure by 2 cm and APAP vs CPAP due to REM events.
During the titration study I only had about 6 minutes in REM stage sleep where my OSA is much worse so they didn't really get much time to titrate optimally.