Also out of curiousity how does the fact ones will never hit skew the percentage? Where if it was simply a normal one there would still albiet low percentage to actually hit. In the case of d&d you'll never hit on a one, and the opposite is true for the 20, and sometimes 19 being that you'll always hit?
In any situation where Attack Bonuses - AC is between -19 and +19, nothing changes and in the situations where it is less than -19 you treat it as if it is at -19, while in the situations where it is greater than 19 you treat it as if it was at 19.
