Every lookup shows you where your coverage overlaps. Not one of them shows you where it doesn't.
The strip between two zones that almost meet stays invisible until an order lands on it. We sample a grid over the catalogue and ask the index about every point, and the misses that touch each other become one named gap. Spacing is the resolution of what you can see at all.
We'd want to hear your test for the places nobody queries. https://shipmindlabs.com/c/e1731228