I attempted to use the mia_exposure_photographic node. But I think I found my problem. Nothing to do with the cm 2 factor. I used linear workflow so for me to see a color corrected image in the renderview, I changed the display color profile to sRGB. I did not set it back to linear when I attached the exposure node. So I had double gamma correction on the output. No wonder it looked flat and washed out.
Earth: The crazy asylum of the universe.