i dont think there is an option for the grass distance ,
farclip is for the objects in the far distance, plantdensity is for the number of plants that appear ( near you not in the distance ) , speedtreedistancescale is for the big trees in general , the ones in the back and how they appear (low / med / high quality once you get close enough to them )
might be the ground clutter thing , gona have to play with that setting to see how it is