Troops wish to join you?

[Metathron]

Well, I'm not talking about scripted events, if that's the right term, just about random troops offering to join you, in the vein of Heroes of Might and Magic. Perhaps it's quite common, but this is the first time it has happened to me, and I've played a whole lot of this game already. I assume the chance of joining depends on the strength of the stack relative to the strength of your army, i.e. your army must be vastly more powerful than the stack offering to join?