They're not linked to the position of the villagers, but when Aaron is sick in bed you can't cast open domain 2 on him at all.To aura-dev:
It should be stated more clearly that portals are linked to villagers, but that the place where the portals send you are linked to the position of the villagers, i.e. it is not strictly a "one villager, one portal, one part of the domain" thing.