Lighthouses have geographical boundaries. During the golden age and the age of decadence, the moots within a particular lighthouse's boundary were powered by that lighthouse, and paid tithes to it in turn. Wayfarers were expected to attend liturgies at their local lighthouse rather than 'shop around' for one they preferred.
The size of a lighthouse is measured in the number of attending moots rather than the number of individual congregants, with people living outside of a moot counted as a moot of one.