Distance Field and Collision Channels

I’m using distance fields (to nearest surface) in my materials to add a blending/dirt effect to my procedurally placed rocks. Due to the requirements of the project, we probably can’t use RVT.

Is there a way to mask by collision channels or something similar to prevent dirt from being drawn underneath a character standing on a rock, or other objects clipping/colliding with it? Ideally we could mask by landscape and then not have the rocks capriciously get dirt added by other near surfaces. Has anyone run into this? Are there other solutions/approaches that might be more ideal?