Okay so I think I think i've created good.....
I already have a use for the shader im creating so this is what I have come up with. I know that I want the 'dispersal' to be fairly random, or as random as random ever is in these situations. So I used a colorised texture in the Occluded color channel. I adjusted my max distance as per your screenshot (im so fuzzy when it comes to scene scale *whole other conversation!*) then toyed with; color spread, the 'calculate from' (which I suspect is tantamount to concave+convex??) and direction offset which clearly relate to X, Y, Z.
This produced the screenshot which is ballpark what im trying to achieve. A rough, random, dirt spattering. I can then duplicate the shader out and change the seed on the colourised texture to produce different results, if that makes sense!
Thoughts appreciated,
Thanks,
Phil
