However if you are a lazy dude and dont yet want to spend time converting the shaders to support fog because you want to focus on doing the super important stuff, you might want to give my post processing fog a try 
probably big bummer for you up front: it doesnt work the way you are used to with distance and density values, instead you define a plane that seperates fogged from non-fogged area and for the fogged area you can define a density factor, however as soon as you’re in the fogged area, fog starts right infront of you (dependant on the density there is no fog though right infront of you) and increases linearly based on the density you provided
it is a postprocessing effect, however it allows fog to get thicker towards the ground and its easier to plug in than converting all the shaders you are using probably