What is the basis for this observation?
Not much rolloff towards the "knee" and then lots of rolloff below it.
The more damped it is, it will usually have a higher knee, a slightly steeper rolloff towards that knee, but a more gradual rolloff below it. Of course equalization will mess with that "natural Q" but I think the frequency response is what he was refering to when he said it doesn't seem damped enough.
Also the less damped a box is, the more it's "spring protected" at lower frequencies too. The spring protection means lower system efficiency, which in turn means that you can end up being amplifier limited which seemed apparent in the power compression tests at lower frequencies. Being amplifier limit ain't so bad in subs especially with all their soft clipping etc. The point is that damping it more would possibly push the 12" driver too hard.
FWIW people seem to subjectively prefer the slight punch a less damped box can give a sub. I'm crazy so my maelstrom will probably have a Q near .57... a rather damped box that does hit x-max if you throw enough power towards it. I wish it didn't weight near 300lbs... I'd take it outside and do some of these ground plane measurements once I got a mic and sound card. I really want to.. trust me.
BTW, I'm considering picking up one of these emotivas to (after decoupling) put high up on a fireplace. I've read that having a source of bass higher up in the air than other bass sources can give good results. The pro is that unlike the maelstrom, it's probably light enough to put high up. The con is that I don't think it could keep up with the maelstrom so I don't know how I would blend two vastly different subs together. My next step is probably going to be to add another maelstrom on the ground.