Ok, so it’s going even crazier…
I still can not find the source of what “Based on display resolution” does. When used, it will always subsample any given default display resolution. It will never use native resolution. This implies it’s probably meant to be used with TSR, as TSR is expensive but can be offset by upscaling from lower res.
BUT what if I want to use “Based on display resolution” scaling with TAA? For TAA, I would still want to subsample for lower scalability presets, but use 100% sampling for the high quality ones. Since I don’t where the “Based on display resolution” resolution scaling curve comes from, I am unable to edit it, therefore I can’t use this resolution scaling mode with anything else than TSR.