Can you illuminate on why this particular grid patter was chosen?
Certainly. There is a lot that went into the decision; but, ultimately, "chosen" is an apt term to apply.
I started with the horizontal and vertical beams seen in the earlier pics. Two problems began to evolve as I moved forward with this idea. One, the placement of the windows began to dictate where the structural members could be placed such that it seemed it would result in a weak design. That nagged at me but not as much as what ended up happening on the leading edge of the dorsal neck. Carrying that design to conclusion would have resulted in more than half the structural load sitting on a single spar in the front. And it would have called for a lot of really odd sized and shaped panels for the skins. So, I pitched that idea, griped, reimported my mesh and started
from the base form again.
From here, I decided the spars should be on the diagonal with some horizontal and vertical members. But, in the process, I also moved
the placement of FJ's windows. He had them almost literally sitting on the floors. I moved them to mid deck level. Did a structural reinforcement with a mid deck horizontal spar and then scratched my head as to how I would handle the forward section. Everhart presented the answer there. So, the design ends up being an interpretation of Everhart. It's not without its problems; but, it's far superior to what I started off with.