Like many things in Elemental, there is currently no file for the combat engine. All of the calculations are handled internally and are hard coded somewhere in the engine. As far as I know there is no way to directly effect the way the calculations are done, but that is not to say that you can not effect the feel of combat. Most items - Weapons, Armor, and equipment - contain modifiers for these values, and the base values can be found in the unit definitions. From my experience, playing with the various unit stats can have a profound effect on general feel of tactical combat.

Now, I will agree that it would be nice if these calculations were placed into the XML in some way, as this would give the mod community the ability to radically change tactical combat, but this is only one wish list item of many. If you feel strongly about this one, put it in the wish list thread in the mod section.

One way you could skew the combat calculations would be to change the attack/defense values of various items up or down to get it closer to your desired effect.  Example:  If you want Strength to be less of a factor, increase the weapons values a bit (double, extra 5 points, etc.) so that the strength bonus isn't as significant.

If you want 'unarmed' people to be a little tougher, design an item that's free but provides 1 or 2 defense.

As soon as Dodge is fixed, there's some possibilities here too.  If you want attacks to hit less often in general, increase the Dodge skill via some 'free' item.

You get the idea.

Not to pimp my own mod, but you might want to look at my Updated Weapons mod as it has a fairly significant impact on tactical combat. Also, you may want to check out gnilbert's mod, even though it is out of date.