The simulator that Johan uses is horrible.
Personally I found this to be easier
http://www.dom2minions.com/Mini.shtml
It gives you a mini map of just a few provinces and two test armies. You start an Era 1 game selecting the Mini map, start as Arcos and Ermor (human players on both), then have the armies both attack then empty province next to them.
Edit the .map file (its plain text) for different armies armies to try other simulations. You can use any units, give equipment, give gems, give spells, give experience. Prior to the combat you can set combat actions to try different tactics. This is a
fairly easy way to test it over and over.