Mask Map - Smoothness Channel Not Working?

For some reason, I cannot get the smoothness channel of a mask map (the alpha channel) to have any sort've effect on the material.

I have exported in both .png and .tga and unchecked sRGB but I cannot get it to function correctly? It just defaults to the slider only.

I have even tried having Unity auto-upgrade a standard shader to an HDRP one to auto-pack the mask map and it doesn't seem to make a difference.

I've attached a screenshot in blender of what I'd expect using a debug smoothness map, and then the same table in Unity (a little hard to tell in a picture alone, but moving along the surface shows no roughness patches).

Has anyone run into this?

 

To anyone running into this same problem, getting photoshop to save a file with an alpha channel when it is NOT a PSD is bizarrely deceptive. I've had more luck with 32 bit targa files as opposed to 24 bit png files.