Hi thanks for replying - I had never thought of taping my mouth, mainly because it still doesn't seem possible that the leak is caused by an open mouth. But what else could it be? Maybe an ill-fitting mask - I know ResMed recommends changing ever six months or so, I imagine it all stretches through use and washing, but it's not feasible to do that really.
EPR was originally at 2, and it was changed to 3 ages ago for reasons I cannot recall. It was dropped back to 2 because apparently you get better control of AHIs with the lower number and this is in fact what's happened - I was usually between 2 and 3, now it's under 1. But I think maybe if there's a high leakage then the AHIs won't be being recorded correctly, but that's just guesswork on my part.
I do not know if there's any correlation between EPR level and leakage. In fact, despite believing I understand CPAP treatment pretty well, I realise I probably don't know very much. And much of the information "out there" can be confusing and conflicting!