I don't like that you manually counted the diamonds and included ones that are clearly beside each other. The whole illustration is a bit of an illusion and I think it's best if we don't assume that certain diamonds made via stacking other diamonds be counted as layers by themselves. After all, it is never explained how we're supposed to view the diagram. Are we supposed to view the diagram as a 2D plane, where the layers are stacked in a way that makes the top diamonds superior to the lower ones? Or are the diamonds stacked on top of each other in a 3D manner, thus creating the pattern we see? Unless the diagram has a clear explanation, I'm not keen on using a manual count of overlapping diamonds as proof of layers.
The 6D is solid though, and even if the diagram isn't clear, the multi-layer part makes me think they can get a "Low 1-C, likely higher"