This shows what a few adjustments does to the mat using the intensity, opacity and monochrome values using a terrain I created in Bryce and imported into z.
I figured out the size problem but had to cut down on the quality of the texture used but it should still work great with terrains and not look good at all on a sphere etc Dont expect this to look decent on anything but long distance shots
More experimenting. I took an old background i made in bryce photoshop and painter, applied it to a 3d plane as a mask, inflated. Turned off the texture and applied the mat. This is a lot closer to the look i want