I use 7 minimum with EPR of 3...so I have 7/4. I like the way it feels. I am sure I wouldn't like straight 4 cm all by itself but with IPAP being 7 I find it quite nice. My AHI is nice and low most nights and when it's not it's 99% because of SWJ due to crappy sleep from back pain so I just shrug my shoulders and move on.
If you are happy with your AHI...and you are happy with the way it feels when you first mask up and turn the machine on and are comfortable...and you sleep good and feel good...use whatever you feel works for you.
My primary goal...good quality sleep as best I can and best chance I can get of feeling decent during the day. Numbers be damned and sometimes graphs be damned.
I did briefly try 6 with EPR at 2...I sort of started to feel a bit stifled...not quite enough
air moving for comfort. I knew what it was and I knew I could probably get used to it but then I figured why should I???

So I didn't really work at trying to get used to 6/4....I am quite happy with 7/4 all the way around...comfort, therapy effectiveness, etc.
I may have to RISE but I refuse to SHINE.