My current approach in my own ACW rules is to have commanders give die roll modifers to unit activation rolls.
E.g. units need a 7+ on 2D6 to activate, but commanders can give a +0, +1, +2 on that die roll when in command range, also depending on type of activation (in my rules: fire, charge, move). A commander can have a M+1, F+0, C+1 profile. Or M+2, F+0, C+0 or something like that. Thus, some commanders favour movement and manoeuvre, some are better to give fire orders, some are bold and favour charge orders. I also have some commanders only give a bonus to infantry or cavalry units.
At the start of the game, a player draws random commanders (I have a pile of 10 cards, see here: https://snv-ttm.blogspot.com/2020/09/acw-house-rules-commanders-and-random.html ), typically 3 or 4, and assigns them to each brigade (1 commander per brigade). The overall effect is that some brigades are better for manoeuvre, others are then better used as a “keep position and fire”, etc.
When a brigade fails an activation, the brigade is done for the turn – but other brigades still can activate (cfr Black Powder and other similar systems). So, a brigade and its commander will on average have more activations if they do what the commander is good at. But they can still do all the other things as well, of course.
Also, it doesn’t make sense to give commanders a – modifier. I rather keep the base number at 7+ , and work with positive modifiers on top of that. But you could do it by having – modifiers as well, of course, but then you’ll have players say ‘I’ll have the unit act on its own, they don;t need their lousy commander’ 😉
I try to avoid having a system that requires a “memory”, e.g. “do this or that during 3 turns to get a bonus”. That requires bookkeeping over several turns, and I don’t like that.
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