However once a shot hits there is a test to see if the target retreats or (in the version I'm playing with) is destroyed. In the basic game this is based on quality - it's 50/50 for a trained unit, with destruction being 66% for a green unit and only 33% for a veteran one (-1 and +1 to the roll, effectively). As recorded elsewhere in this blog I have used a method where the test for retreat/destruction is based on the unit's strength and quality. Units have a basic strength of 2 (Artillery), 3 (Cavalry) or 4 (Infantry), modified with a +1 if veteran and -1 if green. If you roll equal to or less than the modified strength the unit retreats, otherwise it is destroyed. I realised that there was scope for building the effects of cover into that test.
So here's what I'm currently working with. First roll to hit. You need a 5+ on a single D6.
+1 if at range 1 and shooting into the flank or rear of the target
+1 if the unit didn't move (cavalry or infantry)
+1 if artillery firing at the same square and target unit as its previous shot.
If the shot hits, then the target must roll to see what happens. Roll a D6
+2 if shaken (see below)
+1 if Green
-1 if Veteran
-1 if in light cover
-2 if in normal cover
-3 if in heavy cover
If the score is 0 or less then the unit stays where it is but becomes shaken.
If the score is less than the unit's base strength (2-4, depending on type), the unit retreats if it can.If the score is more than the unit's strength then the unit is destroyed.
Adding the 'shaken' effect is the big change here. Simply use a marker of some kind. A unit which is already shaken simply stays shaken; there's no cumulative effect. If the unit is activated or retreats then the shaken status is immediately removed. Essentially the effect of being shaken is that further attacks on the unit are more likely to cause a retreat or destruction. So a unit in cover might need a couple of telling hits to oust them, and veteran units in fortifications will be exceptionally hard to shift.
Why add the shaken status at all? Well, I didn't want a shot that hits to result in any kind of 'No Effect' result. If you score a hit you should be rewarded with an advantageous result of some kind which you can then exploit. Shaken does this, even if you may have to plan how to exploit it carefully, or get lucky with your activation cards.
The nice thing with this mechanism is that modifiers can be applied either to the roll to hit or the roll for effect, depending on where you feel they are appropriate. For example I am thinking of penalising long-range artillery and infantry fire. Initially I thought a -1 to hit would work (and it still might), but a simple +1 on the effect would work too; the shot has the same chance of causing an effect, but the effect isn't as dangerous at longer range.
Anyway, I'm currently playing around with it and will see how it works out this weekend.