Moving-mass and BL over the first 5mm's is very important for efficient mid-bass.
Also, the PA-460 likely has more cone-area because the surround is smaller and thinner and lighter.
The coil is smaller and lighter.
That's why the UM is ~88db/w/m and the PA is ~98db/w/m.
Higher mass means that it is slower to start and slower to stop, like a 18-wheeler vs a Lambo.
Sinewaves and sweeps aren't a good representation of impulse response.
I think you would find that if REW used an actual impulse for the IR chart the result would be a lot different than the derived value it currently calculates.
Ignoring test tones. Music and Movies aren't sinewaves nor sweeps. It's somewhere of in-between the two extremes. It's not an impulse but not a sweep either. It's variable-frequency and variable-amplitude, one doesn't know either until it arrives and the cone is asked to reproduce it.
The acceleration and velocity values of the cone during music are variable.
Imagine an Indy 500 race where the goal isn't to cross the line first but rather to start and stop and re-start and re-stop as accurately as possible (best tracking), regardless of the asked magnitude of the acceleration or duration, and the driver not knowing what instruction comes next, or when.
Full blast into Drive and full blast into Breaking and Reverse. The 18-wheeler is at a massive disadvantage.
This is easily demonstrable by waving your arm. Now increase the excursion to 3ft while maintaining the same speed, and then increase the speed 10x while maintaining the same excursion (or NOT reducing the excursion). Nearly impossible for a human. Too much mass and not enough dilithium crystals captain!!!
^ The cone may be asked, multiple times, to switch directions back and forth, before even crossing the resting-position, on any given side, at any given time!
It's being asked to play multiple different frequencies, at multiple different amplitudes, all at once, and without "coloring outside the lines" in real-time (and without knowing what comes next, at any given moment!)
It's amazing that it can achieve only 1% distortion under those conditions, or even 10% THD!!!