Fogsheet is here:
StaticMesh’/Engine/EngineVolumetrics/Fogsheet/Mesh/S_EV_FogSheet_01.S_EV_FogSheet_01’
Another very cheap but probably better option for your case is the “Falloff Sphere”. This is what we used in gears1-3 for all of the spherical glows around fires etc since it was cheaper than using the actual volumetric fog (which for the most part had to be reserved exlusively for our ink and smoke grenade effects).
StaticMesh’/Engine/EngineVolumetrics/FalloffSphere/Mesh/S_EV_FalloffSphere_Mesh_01.S_EV_FalloffSphere_Mesh_01’
Another option is to use the material function “SphereGradient-3D” combined with “Exponential Density”. That will give you the overall most realistic falloff if you crave it. Although that version seems to have a bug with the “depth fade” option. I am looking into that soon.