i use a PF for every different fake stones. So if i have 4 nodes of 4 different fake stones, i use 4 different PF.
the colours in these renders are the same but it doesn't come from the Fake stones but frome the last surface layer i used.
i am not sure to understand your question about surfaces... now if i use several surface shaders for different part of the landscape (flat ones, vertical ones, etc) i can decrease the coverage of the different surface layers so they can melt...
sorry... maybe you could ask differently your question... i can give you hints about fake stones...