The PPDPO setting in Oculus is equivalent to the OpenXR custom render scale.
Because you are using Oculus, you are using their implementation of OpenXR, so the custom render scale in the Developer Tools will have no effect on your display.
In your case, using Oculus, your “balancing” for FPS, detail etc. should be done by varying the values of Render Scale (in-game) and PPDPO (in Oculus Debug Tool) as you have found out.
I’m surprised with your rig that you are able to run Oculus PPD at 2 - when I was using my Rift S with my 1080Ti, generally anything above 1.4-1.5 would start to push my system too hard. It’s also interesting that you can run Render Scale as low as 40 and still be happy with the details. Maybe it’s because I’m getting old and my eyes aren’t what they used to be! 