One thing I've done occasionally in my spare time is look over detailed battle reports of actual battles in history - famous ones like Agincourt, Cannae, Midway, and others as well. I look over the various troop movements, composition of forces, strategies and tactics used by the commanders. Naturally I do this for our featured time period as well.

One thing I noticed as I read these things is that I don't really understand the thinking behind a lot of the decision-making that happens. So, I look at a particular battle, and I see how the generals maneuvered their guys, and what their tactics were. But I find myself constantly wondering "why did you do that? Why did you perform this maneuver as opposed to something else? Are you unable to use the woods on your flank to your advantage somehow? Why are dedicating your reserves now, as opposed to later or earlier in the battle?"
I question the "why" aspect of battles with distressing frequency, and I don't really understand the thinking behind them. I know about the big obvious things like "don't get surrounded", "protect your flank", those kinds of things, but the intricacies of actual command are beyond me.
I was wondering if anyone had any good resources that go into these subjects. Before anyone asks, I have "The Art of War", have read it (with commentary) at least 2 or 3 times, but that's not what I'm looking for. While a great manual, it tends to be a bit too "big picture" talking about the war as a whole for what I'm looking for here. I'm looking more on the level of an individual battle - how does one decide what the best course of action is, and then how does one actually go about executing that plan?
Thanks to everyone who can offer any help.