The fog definition files for raytracing and the biome fog features only read from the bottom most pack with the files in the global resourcepack listing.

packs above it in priority on the global resource list get ignored, the opposite of how it is supposed to work.

To explain more clearly, with image example.

In the image example provided both the packs "CUSTOM"  and "Kelly's" have fog definitions.

despite "CUSTOM" pack being listed above "Kelly's", kelly's fog definitions are utilized by the raytracing engine.

This had been tested and works in reverse with the other pack.

The game is only loading the fog definitions in the bottom most pack of the global load order.