what´s everyones herald hunting strategy? how do they even work?

So to my understanding, while in a TZ, there is a 7% chance on killing an elite or a champion pack to get a "draw the ire" message. From there on, the herald can spawn in any previously unvisited part of a terrorized map (as in, didn´t go there in this game, not tied to undiscovered map space, in single player I basically have to remember where I´ve been and where not). This distance seems to respect the usual spawnrules of elites/champions, so around 1.5ish screens away, passable terrain or not doesn´t matter. You can get multiple ire messages before running into a herald, and multiple heralds can spawn right next to each other.

So basically, a herald can be right around the corner, or in the next map, or somewhere else (like: ire in arcane sanctuary, herald in stony tombs). It seems to me like everytime you go somewhere and there is an elite/champion pack to be spawned there, there is a chance that this might be the herald, or rather: the herald is added to it, as there is always tons of mobs nearby including elites/champions. Is this observation correct, or am I just seeing things?

Furthermore: heralds have 5 different levels of power/drops inside a single game, increasing one per spawn. Does that mean that after 5 heralds, no more can spawn in this game, or is this just their max level?

How do you farm heralds? Obviously, getting some supersunders would be nice, I´ve yet to see one so far, many times games don´t even spawn 5 heralds for me, especially in act 4 where it´s more like 0-1. Do you enter a game, terrorize an act, run around until you get 5 heralds, then, kill the boss and move on to the next game? Do you use multiple worldstone shards in the same game? Or something completely different?

And is there another aspect to them that evaded me so far?