What would be the best way of blending a mask for vertex painting?

Development Rendering
1

I have a master material set up to be able to vertex paint snow on objects using a mask, it looks fine but I would also like to be able to use one of the object maps to act as a height map and effect where the snow covers the surface of the object. Such as in the screenshot of the stairs, it would look a lot better if the snow mainly painted on the divots in the metal rather than a seemingly smooth surface. I have tried using the red (AO) and green (roughness) channels to combine and then add that to my custom mask texture (see screenshot) but that didn’t work. I don’t know much about blending stuff in UE4 so I’m not sure what node to use.

Would it be possible to use the normal map to drive this effect and somehow blend that with my mask texture?

2

Hmm It’s working ok on some things and not others, probably down to the differences in the objects AO/roughness mix. If I could convert the normal map into a black and white image I feel like that would be a more reliable thing to use, is it possible to do that in UE4?