

What you really need to do, at least in the early game, is accept the fact that your heroes will be over-stressed at the end of every mission. However, only certain hero classes have attacks that can hit the rear positions, and even if you have those heroes on your roster, their long range skills might not be unlocked at the start of the game, and it is expensive to unlock them.

In order to avoid it during battle, you need to have heroes who can hit the third and fourth enemy positions (since the worst stress dealers are usually in the back). Avoiding stress is very difficult at the start of the game.
