So here is my suggested method for setting up your Auto BiPAP. My thoughts are to start simple to establish a base treatment pressure, and then decide based on the results whether more adjustment is needed in a phase 2 of the adjustments. The SleepyHead reports indicate you are currently in a Fixed BiLevel Mode with IPAP at 20 cm, EPAP at 10 cm, and Presssure Support at 10 cm. This does not let the machine do anything, and you have reported that you believe the pressure is too high.
Phase 1
In order to see what pressure works best for you I would suggest switching the Mode from Fixed BiLevel to Auto BiLevel. See page 4-19 of the manual. This will allow your machine to adjust the pressure within a set range. With SleepyHead you will be able to see what pressure is needed to normalize the obstructive apnea, and at what pressure the central apneas start to appear. The DreamStation machine is able to distinguish between obstructive apnea events and central apnea. It should only increase pressure for the obstructive events and not for the centrals. In theory this should keep the machine from running the pressure up unnecessarily high.
The first step is to set the Mode to Auto BiLevel. The Menu should now change to display an IPAP Max, and EPAP Min (The manual says EPAP Max, but I think that is a misprint). See page 4-20. To start with I would set IPAP Max to 15 cm, and EPAP Min to 8 cm.
There should also be a display of PS Min and PS Max. This is the variable pressure support. For the first phase I would suggest setting both PS Min and PS Max to 0 cm. This will force the IPAP and EPAP to be the same. They will both go up and down together between the limits you previously set at 8 to 15 cm.
I would collect at least one night's data with this basic setup and post the results back here. That might suggest some further tweaks to the settings, but the main purpose is to collect some data to find out what pressure works and doesn't work for you.
Oh, and make sure you remove that filter material you were reducing the pressure with. It will mess up the numbers in SleepyHead and also keep the machine from automatically adjusting pressures correctly.
Phase 2
Depending on what comes out of Phase 1, the next step may be to try adding in some Pressure support. It may help with central apneas or it may hurt. About the only way to find out is to try it. But, lets not complicate things, and leave that aside for now to see what comes out of Phase 1.
How does that sound? If you have any questions, just ask.