[Ric Schultz]

I don't know what tweeter you are referring to.  The Neo 3PDR is used by BG Radia themselves on an open baffle and they use 12 db per octave x-overs.  Danny Richie crosses it over using 12 db per octave open baffle as well.  No compensation in any way.  Just look at Danny's measurements.  Look at the baffle of my speaker on the last page.  Same there.  12db per octave.  Measures real good, Sounds incredible....goosebump city!  And we are talking 3K crossovers.

[Davey]

Yeah, I've always wondered about the crossover network in the FS-420 speaker.
I HIGHLY doubt it's a second-order electrical high-pass network on the tweeter at that frequency. 
The other models are all arrayed setups where multiple tweeters alleviate the limited power-handling capacity of the Neo3 drivers.

There's no magic here.  These drivers have trade-offs just like all drivers do.  Removing the rear cup is one of those trade-offs.

Dave.