Yep, that makes sense, Vaidra. Some writings suggest that the fire work kinda like a heat-seeking missile - it targets somebody nearby/nearest shortly after spawning but if the targets gets out of a certan range it re-targets. It could also be that fire spawns, move a bit away from boss and then targets a nearby player.
Any which way it is suggested that if the targeted or closest person runs out of range it can go back targetting the then nearest melee.
There seem to be no hard evidence, but I tried yesterday to wait a bit for some flames and they then, a few times, seemed to lock to me. So if you are confident about your running skill (or your bubble/iceblock:)) then you could try and let the flame hook on to you.