I used a plane set right in front of the camera, with a modified daytime sky material and then just fiddled with the transparency and fuzzy settings. I lowered it into the ground until it was the depth I wanted. I also set the "murky" slider to "clear". I also have about a 15% low altitude blue fog going in the background. Without the plane, the foreground is pretty brightly lit, but the mountain in back is fogged out. What surprised me was that all the blue gunk from the transparencies on the leaves, etc. combined with the plane and fuzzed the whole thing to the point that in the larger image everything has a sort of chalky texture to it.