BBC diffuser depth?

[gdgross]

Maybe I'm just a knucklehead, but I can't seem to find what the depth (relative to the side dimension of those Primitive Root Diffusers in the much-talked-about BBC report. From the photos, it looks like the height of the '1' square is the same as the side, but in the diagram it looks much shorter.

Can anyone shed some light on the subject? I would think that, for example, using 1" squares, that the '1' cube would be 1" deep the '2' cube would be 2" deep and so on, but I don't see that mentioned in the report, and figure 5 seems to contradict that.

Thanks!