I believe the ground vis setting renders objects another 1K out. I think the ground object distance slider thing goes out to 5K, and that groundvis mode takes that out to 6K, but I'm not entirely sure.
I believe it's setup the way it is to avoid a big performance hit from trying to render everything, and striking a compromise between detail and performance. I don't think there's anyway in game to push those distances out, if that's what you're asking.