I tried ticking the setting as you suggested, I have 2 clouds under my atmosphere tab a cumulus layer to create fog in the general atmosphere and a cloud layer v2 for another lower thicker fog.
Ticking both clouds created a much darker scene which honestly shows the lack of detail to the floor which is not ideal...
Ticking only the cumulus layer made the top half darker while retaining the thick fog at the bottom which i think its a good alternative, it certainly helps to bring a more horror vibe that I initially was aiming for.