Thanks bruno, but what I want to achieve is e.g. a single big cumulus cloud on the sky without having to use a Metacloud. I want to see the "profile" of the cloud layer, similar to this picture: http://www.wetterbild.de/wetterrevue/wetterwelten/fabienne/schwergewitter/schwergewitter-Dateien/image039.jpg

So it's not a matter of haze or Aerial Perspective, it's more a matter of "deleting" some clouds in the foreground in order to see more of the cloud profile in the distance.