Inverting a directional near set is a neat catch. One thing I'd want to test is flapping: with a hard cap of 8 and a 3-tile cutoff, two people hovering at the boundary could toggle in and out of each other's allow lists on nearly every tick, causing repeated permission revocations and re-subscriptions (audible as clicks or dropouts). A bit of hysteresis, say entering at 3 tiles but leaving at 4, or a minimum dwell time before dropping someone, would likely smooth it. Did you see churn like that when people stand near the edge of the radius?