Hello. I know this is an old post but, if anyone reading this and having the same problems… I’ve had the same issue and the way I’ve fixed it was by using the Level Blueprint to check de position of the character and depending on that position, Finterp the density of the fog. Also, you can use volumes and check the collision of it, every tick and check if the character is inside it.
This solution doesn’t make you able to do a visible fog cloud in a certain part of the level, but it is a cheap way to increase the density of the fog in certain parts of the level.
Also. If you want to work more. you can make a system of optimization for different levels of lighting quality, for example, what I mean by this is to make the quality settings a bit more custom by you, for example, In high quality lighting you have volumetric fog and volumetric shadows, in medium you have volumetric fog but no shadows, un low you have default fog without directional light shadows and only ambient occlusion.
(You won’t believe what you can get away with…)