This is the formation i use for banish - seems to work very well for me

X - Herja - Cianna
X - X - Main
X - Shayd - Blood
Sub: Thucylcides

Herja does a good job of keeping cerb/baal’s morale down nice and low and allows my troops (lb sets) to skill every round. I keep Shayd as last to fall as you never know if you will get those extra few stuns on him allowing you to deal a little bit more damage.
I must be doing ok with this form as since I started using it I’ve had maybe 3-5 times where I didn’t run straight back into the fight when I eventually died.