Is this the filtering you are referring to?
Note that the filter is the implementation of the Volumetric Light Scattering from NVIDIA’s GPU Gems 3. It actually requires the position of the light in screen-space, but it wasn’t added to the filter, the position coordinates are hard coded.
For my volumetric fog, I use the shadow matrix, that’s why the shadows are properly aligned, but I do use the position of the sun projected in screen-space for the Mie scattering.