Unless there's a specific really bad one you can point us to most the attack charts are setup so that at the low end you might get hit more often but at some point the balance shifts, meaning higher up the chart you are better off with the armor.
There has to be a reason to not wear armor. If all you took was a few extra hits here and there everyone would be wearing armor. "Light" fighters would essentially become obsolete due to the disadvantage they would have.
I almost always play "light" fighters. I rarely use heavier than AT12 on characters unless they are a Knight, Paladin, or something of that nature. Even playing a straight Fighter/Armsman I'll usually go the quick/nimble path rather than the heavy/defensive path. If anything I believe that things are already weighted in AT1's favor. The reason for this is because, from a pure damage taken standpoint, I am often about on par with the heavy fighters. They will usually have 'moderate' damage in a fight that I will usually come out of unscathed or beat to snot. However, I can maneuver far better. Jump, climb, run, etc. So, from my perspective, I'm better off.