A nifty fog effect can be achieved when 'details' is set to 0 and the same image is used as the depth map and the tint color. Sadly once you add 'details' the effect is ruined.
My proposal is a "fog" control.
Essentially, items that are lower in the "layer order" receive an increasing amount of some color.
This has a number of benefits.
#1. More realistic Surface (3d mode) filters (smaller particles should have less depth!)
On further thought I think it should be related to the roughness control. So instead of lessening opacity you'd have a color overlay that would serve to reduce contrast.