Don't have my book in front of me at the moment, but I recall some confusion over the magnitude bonuses. In particular, I recall that the Table that handles the examples starts at +30 for Magnitude 30(?) Hordes, and extends upwards.
Funnily enough, it does not show bonuses for smaller Hordes. Am I to extrapolate that Magnitude 20 Hordes would be +20 to hit?