The story.

setViewDistance 3500; And units and objects located on hill peak (3 km away from) look pretty odd flying in air. To fix that we use something like setTerrainGrid 1. But grass distance and terrain details are changed simultaneously. We were pretty happy with the grass settings and didn't want its distance to be altered (it reduces FPS). Sad fin.

The prop.
Could you make additional behavior of setTerrainGrid with two parameters to get the effect separated? Say setTerrainGrid [1,10] - first for terrain, second for grass