Ah that makes sense. I know there are only very specific situations where a feature like this would be needed (materials being blended that have high contrast ex. gradual buildup of snow on dark asphalt) but any chance of adding some sort of option, either for meshes or materials, that tells lightmass to calculate materials for each triangle instead of just using the uv space? This way you can make sure it’s only doing the extra baking calculations for the mesh instances / materials that absolutely require it.
I know you guys have a ton on your table already so maybe just stuff this somewhere in the “Maybe One Day” folder 