What determines random boss encounter?

[zenga]

So I've been fighting a few months in the same area with the same chars. Usually my chars are fighting like this: zenga 1 west of aerthol, vasco or alt 1 south and trejo 1 east.

In 90% of the times I encounter a random boss, trejo is the sitting duck. First I thought it was due to the spot/location. Never really cared about it, as he is strong enough to kill the boss or to pull up a few escapes without much damage.

After the cap raise I moved up an area (coral wreckage), and guess what. I've only had random boss encounters on trejo (about 12), but not a single one on another char. This while fighting with several alts there (solo) on different spots. I do switch spots from time to time, so my first guess that it is spot located is wrong.

His exploration level is lower than zenga's or vasco's, but higher than my alts. It's really weird why he gets the random bosses

Anyway, I'd like to hear other people their thoughts on this.

I should start by saying: "Please don't hate me for writing this, Jeff".

I have experienced greater random boss encounters when fighting in an area in which I, or usually a group member, has not yet killed the corresponding boss.
Is it possible that Trejo missed a boss kill or two, and that the game is associating that to random bosses in other locations?

[zenga]

In the lower areas that is possible, but not in the level 40-70 area's. Vasco & Zenga have done the quests, whereas trejo never has done any quests. That could be an explanation. Though my alts haven't done quests either.

I noticed similar stuff on my alts. Randomy thought it could be to do with their names...