[Norfleet]

I don't think there's any actual weighting: The morale of the squad is simply the average morale of the squad, with the exclusion of "special" morale (30,50,99) units, which are resolved seperately. Part of the reason your vampire/imp squad didn't rout is because a large 200-man squad must sustain a comparably larger amount of pain and suffering before a morale check is performed, whereas a smaller squad is checked with fewer losses. The cruddy morale of the imps is only slightly bolstered by the nearly as cruddy morale of the vampires.