It's based on the observation that the hub unloads from its top-left corner, and tanks can have arbitrarily large inventory size. So I set up a tank belt where only the two leftmost tanks have roboport coverage, and gave all tanks a big logic request for all sciences. The bots flies 2 tank's worth of distance at most, and the line is barely visible on the screenshot.
In the PoC I'm able to unload all the science for my 98 biolabs (fully beaconed with speed-efficiency pairs, mostly-legendary labs) with most my near-hub roboports staying idle. If I removed the leftover chests I should be able to fit two legendary inserters per belt and restore my previous 100k eSPM.
