Posted here because these only show up in custom maps.
With a 5000 / .5 sec emitter boxed in next to a vacuum maker, and makers running at 4x production I only started to gain ore once I had no more than
83.25 makers at 0 fire speed upgrades
65.25 makers at 1 fire speed upgrade
51.5 makers at 2 fire speed upgrades
41.5 makers at 3 fire speed upgrades
This amounts to an ore rate of -333 which was only observable at 0 and 3 upgrades; the number jumped around unpredictably at other fire speeds.