That's OK, this evening my mind jumped to "hey, that would be a good mechanic for larger/smaller creatures, too." Instead of the giant damage thing I had House Ruled before, give them one step per hit die, so an ogre is +4 steps, hill giant +8 steps, etc, up to a storm giant's +15 steps. This will require three steps above 3d12-2 (1d10 for a two-handed weapon is 12 steps from 3d12-2).
The 18.5 average damage step is 1d8+1d10+1d20-2
The 19.5 average damage step is 2d10+1d20-2
The 20.5 average damage step is 1d10+1d12+1d20-2 <--this is a storm giant with a two-handed weapon.
Of course, this would also work for magic weapons. That dagger +1 doesn't do 1d4+1 damage, it does 1d6. The two-handed sword +3? That does 3d6-2 instead of 1d10+3. The cursed sword -1 only deals 1d4/1d6 instead of 1d6/1d8.
In this case, we should add three more steps to account for a Storm Giant with Two-Handed Sword +3. (I'm evil, aren't I? Thank goodness ACKS only measures alignment along Law and Chaos).
The next step is the fairly obvious 2d12+1d20-2
We're getting really swingy next, with 1d6+2d20-2
And the final step is 1d8+2d20-2, for the Storm Giant you don't want to mess with. The next two steps above would use d10 and d12 if anyone's using +5 weapons. Above that, it goes to Buckets O' Dice - the next step above 1d12+2d20-2 is 1d4+2d6+2d20-4 for 26.5 average damage.