added notes:
if you have connecting raytraced surfaces in close proximity it’s a good idea to disable “lumen reflection screentraces”.
5.3.2+ has a “reflection lightingmode 3” cvar (that is not exposed in the ppv) that will disable the surface cache in reflections, reducing noise. it improves reflection quality if your scene design is well lit, but has the caveat that the “fake gi” in the reflection should be controlled with the skylight as a global ambient boost. be aware it will change the lighting in the real (not reflected scene) too.
if you require volumetric fog in your scene there’s a cvar to “sample fog” in the reflected scene. currently it fogs the reflection properly, but overfogs the real scene.
hope it helps to squeeze.