http://www.therunes.net/guide_ac.html
This is a decent guide dealing with various AC calculations. It doesn't date back to classic but it's still helpful.
It's quite possible that the error in the code has to do with soft caps, which I quite honestly have completely forgotten about. This would explain why only certain classes seem to be experiencing this.
Also, from now on I think people posting should give as much info as possible:
class
level
AC
Agi
level and name of mobs used in example
And approximate duration of fight wouldn't be completely useless either since the longer the fight is, the greater the chance of max damage hits happening.
I for one DO NOT want to see tanks and melee disappearing from the server. Variety is my favorite part of the game and I like to see it in the groups I play with.
Basically, I needs me a meat shield to haste and buff and will do whatever I can to help resolve this for them.