Resmed F20 vs F30 IPAP's

[Lgibson]

My F20 Airfit has been a great mask for me for almost three years, with many nights at 0.0 AHI. I am just now changing headgear and supergluing an open place on the silicone to the plastic. Out of curiosity I am experimenting with a new F30 Airfit. I noticed immediately that my usual IPAP setting of 14 was way too much with the F30, making my ears pop uncomfortably. An IPAP of 11 feels comparable. Does this make any sense? I can see how the greater volume inside the F20 cushion might make a difference in the dynamics. I suppose one might say the F20 was leaking but I think not. 
Thoughts?

[DaveCar]

I cant see why they would be a different part, but did you use the F30 elbow with the F30, or kept the F20 one installed ?
(Im not even sure if they both clip onto each mask)

When I tried a full-face mask (it may have been an F20), I didnt like how it seemed to close down my nasal passage and cause me to mouth breathe. The F30's slight lift on the nose helps keep my nasals open.
Could you be processing the air differently thru your nasal passage ?