I have an S9 VPAP Auto that I was using in the bilevel mode at 20 cm/H2O IPAP pressure, 16 cm/H2O EPAP pressure. When I began to suspect aerophagia (pain in the stomach in the morning) I switched to auto mode with settings of min EPAP=14.0, max IPAP=20.6, PS=4. The Pressure Support of 4 gives me the same difference between IPAP and EPAP pressures as when using in the bilevel mode. These changes reduced my average pressure through the night and improved my aerophagia.
This is the reason that I feel that changing to EPR=3 may help if it is not already there. It would reduce your average pressure without materially affecting your obstructive events. May or may not be enough to solve the problem but worth a try in my opinion.