The problem that has become unsolvable is that now I tend lo relax in my sleep to the point where air manages to escape between my lips, this then has been showing up as large leaks and presumably apnoea events to the Dreamstation.
Adjustments to pressure, chin strap and so on didn't alleviate the problem, so the full face mask was the next step.
Today I have purchased a ResMed Airfit F20 full face mask to replace my previous F&P Eson nose mask ($250 Au.. we do get ripped off in this country ).
I decided to go for the Airfit because it is a silicone mask rather than the memory foam version of the F20.
With careful cleaning and handling I have managed to maintain the silicon Eson mask in good condition for four times longer than recommended by the manufacturer, and even now it is only the head straps that are giving out due to stretching from age.
And I chose the Resmed over the Respironics Dreamwear after reading reviews regarding the noise of the air passing through the tubes down the side of the head, and the perceived changes in pressure to the mask by side sleepers when the weight of the head compresses one tube and air flow is forced through just the one tube.
I will leave the pressure settings as they were for the nose mask for a few days to a week before looking at possible adjustments.
Having lain with the mask on and running for about ten minutes, and swapping back and forth from side to side to see if the mask would stay in place while moving around, I feel I may actually be able to drop the pressure a little at some point in the future.
I also tried scrunching my face up with different contortions to see if I could get the mask to leak, and it stayed secure..
About the only thing I think may occur is that I will end up with a marks around my face from the mask.
So my fingers are crossed that my AHI drops and my sleep improves again.