Watery puddles with Ray Mir?

I have an asphalt surface (simple plane) that I want to add some reflective puddles to. I thought I could turn on Ray Mir then use a cloud texture (with ramp to get good blobs of white) to place the relfective pools across the surface. But all I get when I turn on rmir (?) button in ‘map to’ is the whole surface turning mirror like!

Can I get a procedural to stencil in selective areas of relectivity or not?


Select No RGB in the Map To panel.