In reality, it's quite simple: the more zones of a given type on the map, the stronger the guards. An interesting pattern emerges, by the way, that the same native center on Jebus Cross, which is a decent bonus, at the same time makes the guards of dwellings and Pandora's Boxes with native troops harder.
P.S. In case anyone doesn't know, the zone type and terrain type may not match — on the Balance template on mixed tiles, for example. There can be 10 zone types: all towns plus neutrals. The zone type determines the dwellings and creatures in Pandora's Boxes, as well as the main town of the zone (there may be no towns at all, if the template specifies so).
I tried generating a map with a computer to test it — on the same Diamond setup I placed 8 Castles. The guard of the external dwelling of Monks was 70 Troglodytes, for example; other external dwellings also didn't differ much from the standard. So it's still not very clear :smile32:
