Thanks def, Joris and Adrian

the approach is very simple to dirt using AO, and this should be a quick solution for NL. However.. knowing NL and their ways i'm sure they wanna reinvent the wheel again and come up with a whole different approach to something like this.
The issue with the Fry implementation (at the moment) is that controlling it and knowing what result you will get with some specific setting is close to impossible. The lack of documentation on this feature does not help either.
Anyhow, what i did in all these examples above was to use a 2 layer material with the dirtshader in the blendlayer of each bsdf layer, and then i simply blend between both material layers using the dirt (AO) to get this. Rock in one layer, moss in the other for those mossyrock tests. That's all folks!
/ Max