To continue the conversation from Gitea:
I think it would be preferable to have the diffuse ref ball (aka grey ball) albedo set to 0.18 as it is the standard mid grey value used in every vfx studio.
Additionally, it would be beneficial to include a parameter that allows for a custom value to accommodate various use cases.
PS: “Reference Balls” or “Ref Balls” would be a more accurate name than HDRI preview.