Another "farming" location is at chapter 3, Trial By Fire, when you're supposed to stop the barbarian counterattack.
You get to choose between two alternatives, choose the one where you go in with melee support though with arrows coming at you, BUT, that's the nice part, you will actually take advantage from the arrows.
Easy as peasy, gather some dudes, make them stay inside the red circle, the arrows hit, and suddenly they all have skulls above their heads.
Have fun!