In the absence of other ways of resolving battles within an Campaign using the approach of Engle Matrix Games try these simple rules. They were devised by Arthur Harman but revised by me (Steven Thomas).
The essence of Engle Matrix Games is that they allow you to do whatever you want to, so long as you can make a logical argument. You play a leading general of the period. Each turn you get to make one argument/order about what you want to happen that turn. You can make arguments for your side, to cause problems for the other side, or to change the rules! (No more than one level of rule change.)