This is exactly how depth cuing is supposed to work. It has been a feature since P4 (at least) and does still work with the P4 renderer in P5. In this respect, the manual is incorrect where it says that says that it shouldn't work in renders. Unlike you, I can't get it to work in Firefly, but (due partly to popular demand), depth cuing settings were added to the atmosphere node in the material room in one of the SRs. Bill