how do damage multipliers work?

[deccan]

Boron said:
But you need troops to prevent your mages from routing or to use more than 1-2 SCs reliable .

I was messing around with Black Forest Ulm and I discovered that Vampire Counts are so good because they are all immortal. Because of the "immortal commanders do not rout in friendly dominion" rule, I could make an army of mini-SCs out of them that won't rout when the first one dies.