Oh, you aren’t alone in being unimpressed at how they chose the absolute least rack-mountable design in the recent history of Apple. Maybe a wine rack?
I haven’t been able to find exact dimensions on the internal triangular assembly with daughtercards; but it certainly looks like, given the way that triangles fairly neatly pack into rectangles, they could have put several such assemblies, lying horizontally next to one another, in a single 3Uish case. Had they been so motivated.
