/detailResolution/ specifies the number of pixels in the detail resolution map. A larger detailResolution, leads to more accurate detail object painting.
/resolutionPerPatch/ specifies the size in pixels of each individually rendered detail patch. A larger number reduces draw calls, but might increase triangle count since detail patches are culled on a per batch basis. A recommended value is 16. If you use a very large detail object distance and your grass is very sparse, it makes sense to increase the value.