I don't know - I've heard it's about the boost, but I haven't had a boost and I've done better. I think it's more the swing towards engagement, although I'm not exactly top of the leader board on that either. Admittedly, I had a run of two awful months, so 4x only brings me back into line with where I was before it all went wrong!
My only boost was ages ago, and hasn't done much this month. And it was before the money went up for boosts too.
Saying that, I would love to get something boosted under the new arrangement!