Something else that can make a big difference is where you position Calvin and what level Morale Rune he has.

Other things that can affect the result are:

  1. Positioning your Heroes to minimize the Morale buildup in your really strong opponent by not putting any one in front of him.
  2. Positioning your Heroes so you can kill a strong magic user fast.
  3. Putting a 'sacrificial' hero in front of someone with Piercing Thrust so that his skill attack does not damage other heroes.
  4. Staggering the formation front to back if you are facing someone with Sweeping slash.
  5. The list goes on and on.