I haven't really played with the volumetric spheres much, at least to the point where they're overlapping. In this pic which is something I'm working on, at the left you can clearly see the edges of 2 of the spheres that the volume mats were applied to. There are no volume lights, and the "atmosphere" is just a solid black color map for the sky, and is not volumetric. There is no fog or haze used at all. I think the problem is being caused by the point light at the left with the lens flare. Anyone have any tips for using the volumetric materials in strong lighting and not getting such artifacts?