I am looking for rules (which I could not find in manuals) or personal contributions to the question: how big a creature can you entangle with entangling breath? Should it depend on the size of the creature breathing? Should it depend on the area of the breath? on the amount of damage dealt by the breath?
For example, I have a Dragonfire Adept with entangling breath and I don't know which size of monsters he can entangle with its breath. Now he has a 15ft cone breath, he'll get to 30ft in some levels.
I don't think a 2d6, 15ft breath attack should affect a Huge creature, but, at higher levels, I can expect that a 6d6, 30ft breath would.
So, is there any rule that I missed that determines this? If not, do you have (balanced) suggestions?