Exhale relief on a Respironics machine (either AFlex or CFlex) is similar to EPR on a ResMed machine but not exactly the same.
It isn't a per cm drop of pressure per setting like EPR is.
Instead it is a drop in pressure during exhale that depends on the flow rate or how forcefully a person breathes.
The greatest amount of drop is 2 cm at the setting of 3 and that is only if a person breathes rather forcefully. If they tend to be a shallow breather the amount of reduction during exhale is even less.
So the amount of reduction during exhale is dependent on flow...it's flow based and not a straight per cm drop like it is with ResMed machines.
There is also a bit of a timing thing...timing for when the pressure drops for exhale and starts to increase for inhale.
I usually tell people to try all the settings available for any Flex relief and pick the one that feels most comfortable to them in terms of matching their own respiration.
So try the 3 settings and also try it with Flex turned off.
When I experimented with the various Flex relief settings...CFlex...couldn't tell any setting made any difference so I turned it off. When I tried AFlex I found that the setting of 1 seemed a bit slow like I was breathing too slow and the setting of 3 made me feel like I was breathing too fast but the setting of 2 matched my own respiration pattern perfectly...so I elected to use AFlex set to 2.
I don't think that AFlex is available in cpap mode...I think that is only available in auto mode.
CFlex was the very first flow based relief...then AFlex was introduced a little later.