I'm not sure if any of the developers have seen
this thread before, but it might give you some insight as to how aggro worked on live (at least, when the tests were performed). We could use this knowledge to help create a more accurate formula for aggro on eqemu.
Background: The wizards at graffe's decided to do some tests on aggro using concussion to determine how the spell worked. Concussion was used since a) it was of interest to wizards at the time and b) it provided a known aggro modifier and was completely under the testers' control.