Didn’t someone prove about 15 years ago that there’s an oval shape that packs tighter still? Given the hollow core that could probably be done, but cylinders are probably easier for the assembly line to handle. So then it comes down to whether that space is being utilized (for cooling, or weight per cubic inch of the support structure).

I think there are a couple companies with hollow designs for improving surface area for cooling, or at least patents around it.

I didn't mean to say the two packings were the same. 90% is better than I thought circle packing was though, I've mostly seen multi-scale packing used in thermal pastes and stuff and it is probably a bigger difference in 3d sphere packing.