Oh they most definately get the negative supply traits. Like most players I train younger FM's in Rome and at that early stage I do not want the attuned govenor trait so I will move them out, sometimes I forget them and after a while they are eating their bodyguards!!
Also I don't think forts have any impact, I've tried stationing FM's in a fort just outside Rome and slowly but surely they start eating each other, move them back into the city and it's ocelot's nipples allround.
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