Skill20: Margin and Damage Spikes

I recently started a new sandbox campaign for my alpha testers and saw in practice how much damage can spike due to my Margin of Success rules. An opponent that has a 50% chance to hit can spike up to an extra 10 points of damage and average about 5 extra points of damage. This led to some ugliness when a handful of goblins with d4 damage weapons got a couple of lucky hits.

Characters with 14 or 16 hit points figured on being able to take a few d4 jabs over the course of the fight, none of us realizing the average damage going to be 7-8 and possibly as high as 14.


While I managed not to kill off any characters (though one player got to try out the dying rules), I realize I might need to mitigate damage a bit, even though the spikiness is, IMO, more realistic. And I need to do it in a way that won't overly complicate things.

Ideas:
Go On The Defense
My players had asked if there was a way to go all out defensive when they realized they were in trouble. Using a defensive maneuver that gives +4 Melee Defense reduces the odds of being hit and the margin. Assuming a 50% opponent, an opponent that hits now would have an average margin of 3 and a max of 6. I am debating halving the margin damage done to a character using this maneuver, though I may make that a feat.

Improve Armor
Right now, armor is pretty straightforward. It gives DR, ranging from 1 to 6 DR. While upping the DR would be easy, I don't want plate mail tanks clanking about the battlefield immune to harm. I'm considering adding a bonus to Melee Defense, as that would reduce the margins. But I don't want it to get too high... see aforementioned tanks.

Cap Margin Damage
Another idea would be to limit margin damage to the maximum of the weapon. That would cap a d4 weapon to +4 damage, and a d8 to +8. So far I like this idea the least.