An Expansion of the Touch AC Mechanic

[Maat Mons]

In D&D 3e, you have both a touch AC and a regular AC. The idea, roughly speaking, is as follows:
If the attack roll is less than your touch AC, the attack misses.
If the attack roll is greater than your regular AC, the attack finds a gap in your armor.
If the attack roll is between your touch AC and your regular AC, the attack strikes one of the spots covered by your armor.

This could be an interesting mechanic, but almost nothing in the game cares about the distinction between bouncing off your armor and missing entirely. And the things that do care about that instead don’t care about the difference between slipping between the plates of your armor and just punching through the armor. One way or another, the middle result just gets folded in with one of the other results.

I’d like to float the idea of making that middle area matter. There have been various homebrew and even official variants that apply a reduction to damage taken based on armor. So here’s the thought, if the attack hits your armor, you apply the damage reduction from the armor. If it misses entirely, you of course take no damage. And if the attack finds a gap in your armor, you take full damage, with no reduction from the armor. What do you think?

I’m also thinking about mixing this with a system whereby armors provide a penalty to your touch AC, rather than capping it the way current 3e armors limit how much of your Dexterity bonus you can utilize. So as you move to heavier armors, you get easier to hit, no matter who you are. Not like it is now, where the only people who get lower lower touch AC from wearing heavier armor are the ones with high Dexterity to begin with.

As for the amount of damage reduced when the attack hits the armor, I was figuring it would vary depending on your specific armor. I’d be inclined to have one value for all plate armor, another for all mail armor, and a third for all cloth armor. I suppose you could slip leather in between mail and cloth, if you think leather should continue exiting in the game. The only thing that bothers me is that, historically, it wouldn’t be out of the question for some to go into battle with, e.g., plate covering their torso and mail covering their arms.

Thoughts?

[Morphic tide]

You'd need to have the damage reduction scale directly by Armor bonus to cover Enhancement to Armor Bonus, the Bracers of Armor, and Natural Armor. Differing defensive value by material could be handled by splitting the range based on the material in question, while Special Materials could be applied only to the relevant "part" of the range. Natural Armor's damage reduction value would probably need to be a ratio of itself, as Hit Dice, Constitution, and Dexterity are all very askew. Shields would need to be completely reconsidered to work on this model for consistency's sake.

A completely separate way of handling it from your proposal would be having the unmodified d20 roll and Armor tied to body slots for a hit location mechanic (using confirmation roll for crits), dividing the "Armor Bonus" between how much is covered and how good that coverage is. This also makes piecemeal armor and called shots trivial, but does demand a lot of number-crunching I'm not sure how to do to keep Natural Armor from going pear-shaped and magic items are much more annoying. Shields here are fine in their current case as general AC that doesn't apply to Touch.

Combining the two would be either a simple "glancing blow" handwave or another round of complicated number-crunching to keep it viable, as you can't rely on the other body parts to drive up the total for sensible damage reduction values in the late game. In any of these cases, you could separate the value of other AC bonuses like Deflection or Insight by whether they move the attack to better-protected parts or not in addition to the Touch or not case.

[spectralphoenix]

I'd be a bit concerned about how well this would scale. Heavy armor users' touch AC generally doesn't improve much - a first level fighter probably has 11 touch and 15-17 regular AC, while a 8th level fighter probably has more like 12 touch and a regular AC in the mid-20s. Anything that could possibly threaten him in the original system is going to always hit his touch AC.

[Morphic tide]

I'd be a bit concerned about how well this would scale. Heavy armor users' touch AC generally doesn't improve much - a first level fighter probably has 11 touch and 15-17 regular AC, while a 8th level fighter probably has more like 12 touch and a regular AC in the mid-20s. Anything that could possibly threaten him in the original system is going to always hit his touch AC.
That'd be what moving from "Max Dex Bonus" to "Touch penalty" is for, and my point regarding needing it to be per-armor-point instead of a binary. While he might be "hit" nearly every time, he ought to have DR such that he's taking similar damage. Up at level 17, a Marilith's going to do much less, while the sample Frost Giant Jarl is going to be going hard on Power Attack.

[nonsi]

Suggestion: if you hit the armor, DR equals diff to bypassing armor completely.
Seems universal and relatively simple to me.