...I am certain that my fps are unaffected, unless it takes time before the change takes affect?!
The FPS changes from switching ASW on and off are instantaneous. Press Ctrl-F to see the frame rate in the ED monitor window; the number is the raw frame rate, you will ALWAYS see 90 refreshes in VR, hence the difficulty in seeing any actual drop).
Mode 1 disables ASW and only ATW will create synthetic frames when the frame rate drops below 90fps.
Modes 2 and 3 will drop the ED frame rate to 45fps max, without/with ASW support forced.
Mode 4 is the default where ASW will turn on and off by itself. In ED, it tends to turn on a bit too quick and stays on, especially on planets and in stations/ menus.
I always turn it off as it does tend to get stuck on, even in areas where my 1080GTX will happily crunch a solid raw 90fps out. The ASW threshold is set too conservatively imo.
I regularly use the oculus config tool for pixel density...
You don't really need to - ED has the HMD Quality setting in the graphics options which is the same setting as the Pixel Density in the Debug Tool. Unless you're using a custom setting for the HMD Quality and not the 1.0, 1.25, 1.5 etc listed in ED?