I also realize this has been discussed already, but I can't really seem to find the thread, and I think it was off-topic anyway.
After tampering with the bosses' stats in the HAM, I've noticed that all of them exhibit some unnatural behavior: they have a low tendency to teleport, and they don't play their perpetual sound. They still play sounds assigned to "see" and "attack" in single repetitions, though, and attack and move around normally (if they are capable of moving, that is). Sometimes they cloak, but they remain cloaked for a while then return to uncloaking. That way they can sit in the same spot for long enough to be killed from the distance.
However, sometimes they "awaken" and start doing all the things they should be doing, including frequent teleportation and start playing their perpetual sound. I'm not sure what it takes for them to "awaken", though. It seems to happen randomly, flying really close to the robot may have something to do with that. Anyway, the awakening is signalled by the boss' first teleportation - once that happens, a more aggressive AI routine seems to be loaded and the robot starts making the constant sound and teleporting around.
I played one or two bosses in Descent 2 with a regular HAM with only the sounds modified, and it seems the robots don't have such problems as the diminished tendency to teleport doesn't seem to exist. On the other hand, the only stuff I've modified for those robots is strength, sometimes weaponry, boss flag (to alter their resistances) and the number of plasma blobs they give off after being shot with energy. Could one of these parameters have tampered with the robots' AI? The occurences are still pretty random to me and their cause is difficult for me to ascertain. Some bosses work well right off the bat, some take time to awaken and some keep their dumber AI routine right until they're destroyed. Has anyone had the same problem?
Descent 1,5: Level layouts done: 29/54 Secret level layouts done: 0/6