It depends on how you set them up. I think because of the constant whining of years past (as they would constantly fight to the death) that they now need to have an advantage before wanting to engage. In the same token, if they are damaged they would rather run than stay and fight.
Basically to make them fight, make a group of enemies with far greater #'s than your own flight, they will attack you virtually every time, until, again, they lose that advantage.
At least, this is what I've seen.