Can you tell the diff between AHI 4.7 and 2.9?

That's hardly a scientific observation. It would take a controlled study to find out for sure and how you "feel" is subjective. There are many factors that go into it.

Interesting discussion.

I can't really feel any difference at all with APAP.

My sleep study showed an AHI of 20.5 I think and it is now tracking around 3 with APAP.

But if I have a night at 6 or 7 I don't feel any different.

My mask leak rate is 0.06 l/s which is pretty good from all accounts.

I also use my SPO7500 once a week and it consistently shows Sp02 above the 95% level for about 97% of the time and an Sp02 above 90% 100% of the time so I know the therapy is working (I had Sp02 in the 80's a bit in my sleep study)

I don't really see there is anything I can do to control my AHI. I could try straight CPAP I guess but I really feel no different than before APAP anyway.

Mr Random,
Here are some leakage rates, from the manual, for the Mirage Quattro FF mask. Pressure (cmH2O) Leakage rate (+/- 6 L//min)
Pressure= 4 Leakage rate = 22
Pressure= 8 Leakage rate = 32
Pressure=12 Leakage rate = 41
Pressure=16 Leakage rate = 48
Pressure=20 Leakage rate = 54

If your leakage rates are in the mid to low 30s with pressures between 8 and 12, it seems they are within the expected ranges.

Mr Random,
You can get a pdf version of the user guide for your Quattro at http://www.resmed.com.