Currently in the latest 1.16.5 version "1.0.2" optifine's fog start option doesn't effect the actual starting distance of the fog.
Is it possible for the option to be added into the mod directly to allow for a customizable fog start distance similar to the option found in optifine?

not possible since optifine is closed source

No no not a direct compatability option with optifine or anything I was just requesting a fog start distance configuration in the config file of this mod. completely seperate from optifine.