FRUSTRATING mechanics!
I've also found that the options provided for individual unit upgrades don't seem to have a very great effect on how those units perform in combat (even when they are experienced, undiluted veterans of several battles). After upgrading my "core" regiments' (the units of swordsmen, handgunners, and halberdiers that you either start the game with or acquire very shortly thereafter) armor, weapons, etc, they actually seemed to fight WORSE.
My overall impression is that "Battle March" has overcomplicated the systems that worked 10 years ago on the previous games without really adding anything that makes up for the hassle. The older games, "Shadow..." & "Dark Omen" had a decent learning curve to them, and some of the battles required several replays with different regiments, different deployment strategies, etc...but that was what made those games appealing to me.