Right now it's possible, as happened to me, for a ship to end up with a pile of extra items - For example, 100,000 concrete. The mod doesn't seem to take that into account afterwards, meaning the ship ends up overfilled. I have two suggestions, therefore:

1. It'd be great if you could configure the mod to drop off extra materials (either at the destination or origin planet)
2. Look into why that's not being detected and the ship is being scheduled for more material than it can hold.

Thanks!

Great report! #2 was a real bug, fixed in 1.10.4 / 2.1.3. The mod was using a ship's total hub slots as its capacity instead of its free slots, so it ignored what was already aboard (fuel, ammo, repair packs, your own requests, leftovers) and scheduled loads that couldn't fit - then waited for a load that never completed and timed out.

The pile builds up because rockets are all-or-nothing: a request that isn't an exact rocket multiple over-delivers slightly, and since the source planet exports concrete it never requests it back, so leftovers ride along forever.

I skipped the auto drop-off for now - the mod never inserts or removes items, and "dump anything unrequested" would also bin your fuel and ammo. Note the fix prevents future overfilling but won't empty an already-clogged ship; it'll now show as "nothing loads" in the Monitor. To clear it, add a concrete request on any planet's landing pad and it'll get pulled off on arrival. 🙂

If I could make a suggestion for #1 then: Check what's in the users requested slots and construction slots, and ignore those slots when it comes to emptying, otherwise create min/max requests of 0 for the items that are overfilling the ship - Maybe also increasing the number of trash slots, since it'll take forever to unload in that scenario? Or a temporary request on the ground?

Appreciate the detailed thinking and you've spotted the real snag yourself: only the genuinely-unrequested residue should ever be touched, never your fuel/ammo/requests. That's exactly why the mod stays hands-off: by design it never inserts, removes, or trashes items, only sets schedules and its own requests. Every auto-eject option risks binning your fuel/ammo (a 0 request doesn't push items out - the eject is "trash unrequested," which is the dangerous bit), and on a platform that cargo drops onto whatever planet you're over.

Detecting the residue is easy; removing it safely is the part that breaks the rule. So the clean fix is your ground-request idea - put a concrete request on any landing pad and it'll pull the excess off. The clogged ship now also shows as "nothing loads" in the Monitor. If it gets common I'd rather have the Monitor tell you "unrequested cargo aboard: X" than start throwing items overboard automatically. 🙂