Once Clout cards activate, you choose the position of the summoned assist. Vigor attacks first target the top assist, then middle and finally the bottom assist. So the top position could be considered the "front" row, and bottom being the "back."
It's going to be tricky balancing Clout cards. Offensively, they'll constantly attack on their own, likely providing much more efficient damage/Mana than offensive Vigor and Psych cards. Defensively, they'll protect the player from damage. It's really easy to make them too powerful.
This battle theme's way too good to be used for normal situations, so I'm planning to save it for a boss I'll be particularly fond of.