The surface type is controlled by the Physical Material you assign to the material. But the problem is, I think the different surface types are hardcoded.
For instance, open up any of Epic's physical materials, and there's a property called "PhysicalMaterialProperty", and under that is "MaterialType". It's just a text string - "Stone", "Metal", "Flesh_Human", and some custom ones for vehicles.
If you can figure out how to modify those defaults, then you can create a new physical material and assign it to your material.
If you figure it out, let us know!