I'm just using exact formula because math is so much better for explaining these things than natural language. I fully expect you to do a completely different one, but as long as the general idea is preserved it's all gravy.
As for early armor being useless, I was just using 50% all over the place to make it easier to follow the math. In a real scenario the numbers should be balanced so that even low q leather is much better than no armor at all. The delta q modifier might need to be clamped to a bit smaller range, too, originally I wanted to go with 0.75 - 1.25 armour multiplier but feared that everyone would think it doesn't make q important enough. Anyway, the point is that with this system all armour can be balanced to be useful, unlike with the current flat reduction system (reducing 30 damage is next to useless against a sword, but OP against bats).