Moreso I think what throws me is that in your example, the FCC cubes are tilted. (i.e. if you build a FCC stack starting with a grid of squares rather than tri

Moreso I think what throws me is that in your example, the FCC cubes are tilted. (i.e. if you build a FCC stack starting with a grid of squares rather than triangles, it's much more difficult to visualize where the closely-packed triangles lay.)