I saw the firing range slider in the first demo. I thought about it a while, then ignored it.
The problem is, if you open fire at a shorter range than the enemy, it's likely that you'll never open fire because you rout first. If you open fire at longer range, your shots aren't effective enough to start the "rout timer" on the target unit (bottom of the unit info box, red numbers when it's active).
While I didn't actually test it myself, CvC did, and found this to be the case in the game as well as in theory.
I suspect it will be more important when we get some rifle armed troops who can inflict damage at a longer range. It doesn't seem to do much for musket armed troops.
Hook