Looks like this configuration would allow the highest density of units to be fabricated per given surface area. Notice that the hexagon is just barely larger than the wing span where they approach each other. Can't do the math now, but it's likely more space efficient to use the hexagon, than a plain rectangle. You'll need to use one of those shapes so you can tessellate without lose. The carbon fiber structure might not have to be continuous, though I suspect that it might play a role in positioning during fabrication.

They showed a lot of them grouped together into a sheet towards the end of the video, so I assume the hexagon was just a prototype or made specifically for demonstration. Although if you're talking about margins between them on the sheet, I'm not sure.

Like everything, this will be refined over time. Give them a chance!!!!!!!