Hrm I think we'd have to think about this some more. You don't want the values going over 100%

We want something that:
1. if you are close in agi usually hit
2. if you are very far below almost never hit
3. if you are very far above almost always hit

So maybe something like this
chace = 50
if (target.agi < .5 * this.agi) 
      chance = .33
if (target.agi > 1.5 * this.agi)
      chance = .67

but for now it should be fine.