The entire formula for shooting strenght of a unit should be in the manual, but the number of men in the unit is one of the factors.
Based on that shooting strength formula, the unit then scores a number of hits, both the likelyhood of which, and the amount of casualties each produces, you can adjust.
If you change the scale, particularly when reducing the time/turn you'll have to tweak those settings accordingly.
Overall, the system is rather abstract, and doesn't scale down too well - certainly not to the level of where one combat phase represents just one combat action like a single volley.
no truth - no justice
all false belief
blinded by morality
there shall be ... no peace