Which speakers sound good at Low Levels?

I've been downsizing & have recently been using a tiddly pair of Ruark Epilogue. Clearly they are no match for some of the speakers I've owned, but I have noticed they are surprisingly good at low level. Some of the speakers I've had sounded incredible at gig levels, but flat as a fart at anything below that (Tannoy FSMs for instance).

What parameters contribute to a speaker performing well at low level? Can't be efficiency, because all my big speakers have been more efficient than the little Ruarks.

Is it just Size?

Continues HERE