Don't blame it all on small ball. Blame it on cohesion.
First, this team has routinely played with smaller lineups that included James Posey and Mikael Pietrus. If they could be successful with it then, it's certainly not small ball's fault they are losing now.
Second, it's not like Brandon Bass is much of a power forward. He's undersized and doesn't particularly rebound well. He also offers no shot blocking. So let's not pretend that when we go to Jeff Green at the 4, we're losing a lot of "big man" skills.
I think the biggest problem is defensive rotations and figuring out how to distribute shots.
The latter problem was always a problem in the Big Three era, but it was mostly limited to how to divvy things up amongst Paul, KG, and Ray. Now it's how do we divvy up shots amongst PP, KG, Rondo, Terry, Green, Lee, Barbosa, Bass, and Sully.
I don't think it's a matter of selfishness; in fact, it might be the opposite. It seems like everyone (minus Barbosa and Pierce in the Miami game) seemed to defer to much.
But this can be resolved.