Hardness Texture for 3D Model

Hey.

I've just recently completed a specular texture by following the way an author for a Blender book has done it. I'm now trying to do a hardness texture, but I can't seem to get something right. They've got their specular texture grouped into a folder called 'Hardness group', which is inside the hardness texture folder. Then, an exposure adjustment and layer mask were snapped to that folder, which is somehow supposed to make all the shapes black against a white background. I'm not sure what they've done here to achieve this because when I do it, everything goes black for me. 😕😕

Theirs:

Their layer mask:

Mine:

Any suggestions?

Thanks.