Game Development Reference
4. StartDistance controls how far away the fog begins to render. Plugin a StartDistance
of 300 with a Density of 0.05 , and you'll see right away how this parameter works.
You can get a variety of efects out of a HeightFog actor. Ulimately, the look you'll want for
your fog is ied closely with the lighing and post processing that you apply to your scene, but
these examples should give you a good staring point.