Honestly I am surprised nobody talks about aggro range of boss encounters, as different fights have significantly different aggro ranges (ex.1: P8S 2nd Phase his initial aggro range is shorter than his target range, ex.2: the aggro range of Adelphel and Grinnaux in Dragonsong's Reprise is extremely short, you can walk very closely and to their corners even), which people may want to utilise for their openers, like "can I safely walk up to the boss and just faceaggro it or do I have to use a ranged attack"? Latter applies to bosses with ranged auto attacks, which can decimate a dps / healer if they get hit.

Some bosses also do two auto attacks at the start for some reason (Hephaistos I and Voidwalker for example), which is why it might matter as well.