I will, if I ever understand what exactly is causing it. In EA I once went through every single lumen CVar one by one, trying to understand what they did. I seem to remember a ‘reference mode’ that significantly increased the number of radiance probes while disabling denoising, and that improved quality at the cost of a performance nosedive.
I suppose it’s partly a use-case question. I’ve discovered that for offline, Lumen is excellent as a sort of viewfinder for pathtracing, allowing quick but imperfect iteration. Lumen and the PT largely match on medium and large scale, but I’ve noticed lumen struggles a lot with objects bigger than screen-space but smaller than the surface cache can fully pick up, like your situation.