Hi, @AlansArtLog!
My only question is what’s the reason this can never be made to work with overlay mode?
In the lightness mode we create a separate heightmap layer for the paint thickness information. If we want to support overlay mode, we’ll have to make the whole layers stack merging engine to take this heightmap into account and generate that for the merged image. That would mean a huge amount of work with quite disputable outcome. So I decided just to disable Overlay mode for the Lightness mode 