SteamVR at 100% is low enough it won’t have any impact, or rather would be hard to see as you’re undersampling what your device could do (which device?).
SteamVR on WMR devices just reports ‘SS 100%’ below what it is capable of to make more games run smoothly. On the default ‘automatic’ mode of SteamVR it will pick an upscale resolution based on your system performance (say, a Nvidia 1080 class card would be 150% SS in SteamVR). When you put a custom resolution at 100% it’s lower than the difference in back-buffer size set by renderTargetScale would use.
For an Odyssey, native panel resolution on SteamVR is about 212%. On a HP Reverb it seems to be about 188% (I don’t have one of those though). If you set values like that and then try to use it on 1903 then you’ll never actually get to panel resolution, because of the bug.
Acknowledgement of the bug and the plan to fix it on 1903 from Microsoft here:
Plus more background info on why SteamVR picks those values and how to calculate the true native panel resolution - VR News: HP Reverb - Second Gen headsets are on the way - #266 by fearlessfrog