The question is can you not invade in LoC mode which will give you the same hp as the Host? If you can, than that eliminates the problem of unfair duels. Which basically equals it to Human form from previous games.
I heard that the bonus comes from the Lord of Cinder mode which is activated when you consume a Ember. And the host has a hp bonus? I couldn't participate in the stress test but I've gathered this much from what I read around.
So, you cannot invade a host that is not in a co-op state.