Terrain mask map not working?

If I understand correctly, the RGB and Alpha channels of the mask map are to be used for AO, height etc.

However, setting a mask map (created with AO in the green channel, detail in the blue channel, etc) changes nothing in the terrain texture.

What am I missing? Any help would be appreciated. Thanks in advance.

If you are using the Built-In Render Pipeline and not the HDRP or URP (Unity 2020.1.17f), this means two things…

  1. The Mask Map is not used with the Built-In Renderer only the HDRP and URP. I expected the feature to hide if it’s not available, but not in this case.
  2. You can add the Smoothness map to the alpha of the Diffuse map. There is no metalness map, you must use the slider.

This was tricky to figure out because the help documents don’t explain it fully. It says the Diffuse Alpha has “different” uses based on renderer and shader, but doesn’t list the differences.