4 to 20 isn't a "setting"...it's the machine default settings from the factory. That's all it is and not being comfortable starting out the night at 4 cm is a common complaint. We won't suffocate at 4 cm but it sure can feel like we are.
Most people find they need at least maybe 6 cm starting point to be comfortable with the air movement.
You really need to be using OSCAR and see what is happening and determine even if your therapy is optimal.
OSCAR
https://www.sleepfiles.com/OSCAR/
http://www.apneaboard.com/wiki/index.ph ... stallation
http://www.apneaboard.com/wiki/index.ph ... rpretation
viewtopic/t158560/How-to-post-images-for-review.html
For all you know you could still be having a lot of apnea events during REM because the machine can't respond well enough from that 4 cm starting point to prevent the airway from collapsing. You might need a LOT more pressure just in REM than you are getting. These machines don't increase the pressure in the blink of an eye. It takes several minutes of gradual increase and sometimes while the machine is increasing the apnea events still happen.
I suggest considering changing that minimum of 4 cm to maybe 6 cm.
Add in EPR set to full time at 2
and see how it feels and if you are more comfortable.
If you don't know how to do that it's all explained in the manual.
https://www.respshop.com/manuals/ResMed ... %20her.pdf
I may have to RISE but I refuse to SHINE.