Quote -  Thanks a lot, folks! 

Chill, I think I have a recipe for Mammatus clouds. Will try to include such a file. However I am afraid this is one of the cases where the changing the AP setting to something else than 1 will require you to retweak quite a lot of parameters in the FE (if you are heading for realism).

'Often' not 'always'   

I usually crank it up when I'm after a very hazy look or if don't want huge terrains.

Gill