Odd response to changing mask cushions

Here's something odd that I noticed, and thought I'd throw it out there to see if anyone else had ever had something similar happen:

Normal: Hybrid mask, small mouth cushion and medium nose pillows. Modified by cutting off chin flap and using elastic band to hold nose pillows in better. Zero leaks (flat line), nightly AHI average of 0 to .5 for the past several weeks. 95% pressure usually 13.4. Max pressure was usually 13.6.

Changes: Mouth cushion wore out, and being cheap (frugal??), I decided to try different sizes to see if I could utilize the other ones that came with the mask. So I switched to a medium mouth cushion and large nose pillows, same modifications as above. First trial was a 2 hour nap and had an AHI of 2.0 with zero leaks. Thought it was a bit weird, but not a big deal. For the next three nights, my AHI was around 2.0 with zero leaks. 95% pressure was normal at 13.4. Max pressure was normal too.

More changes: Last night I put medium nose pillow into the medium mouth cushion and my AHIs were back to normal at .5.

Conclusion: the larger nose pillows caused my AHIs to increase. Why would bigger nose pillows cause my AHI to go up so much? Granted, 2.0 is still considered good, but that means about 16 - 20 incidents per night versus my normal zero to 1 or 2 incidents per night....that's really quite an increase.

This obviously isn't a problem because I can just use the medium nose pillows. But I'm very curious as to what would cause the change in AHIs, particularly because the leak rate was still zero. Is it possible that larger nose pillows changed how the air pressure was working?

I just hate not knowing.....

Weezy