However, the difference is limited to the value of the better leader. This seems to fit the historical outcome pretty well. The full combat rules are available as part of Richard Fluck's rules translation on his website, so I only give a quick overview. Basically, in each round of combat each player rolls a die to cause losses to the other side depending on his combat strength. Artillery combat strength is modified according to orders and terrain per the following table.
Artillery counts zero in mountains.
In addition, fatigued attacker units are halved and entrenched defenders are doubled.