In cone tracing you sample a prefiltered geometry. (mipmaps)
Depending on radius of cone change to lower mipmap, thus when it hits you get sum of all information in the smaller voxels down the mipmap tree.
This is the reason you do not need to shoot so many rays/cones this way.
Older papers give more information on their cone-tracing..
Is it possible to do cone tracing on polygons?