Coaxials - Reality vs. Experience?

@erik_squires The main design objective/benefit of a D'Appolito array is to mimic a point source. Benefits that inherently follow are higher power handling (plays louder) and lessening of the potential impact of floor and ceiling reflections due to two drivers producing the same frequency range. The design doesn't actually reduce vertical dispersion, just potentially helps alleviate some negative interaction of the floor and ceiling. Before the D'Appolito array the only way to mimic a point source was to use a dual concentric driver (with its attendant pros and cons).

One downside of the D'Appolito array is the tighter vertical listening window created by the three drivers (five drivers in my fully active 3-way design)(seven drivers in the Duntech Sovereign). It just so happens that the symmetrical drivers couple optimally at a certain distance........which you are calling "narrow vertical dispersion" and as a "benefit" It is not a benefit, but a downside. There is no free lunch, each design has its pros and cons. You get the benefits of that narrow window of optimal coupling when in the sweet spot, and the downside of potentially less coherent sound outside of the sweet spot (in reality...not so terrible).

Unfortunately, we can't give full respect to the details in this short response form. 

Please explain "off plane axis listening".

which you are calling "narrow vertical dispersion" and as a "benefit" It is not a benefit, but a downside.

I absolutely disagree.  In a brief reading of articles online you'll see that the horizontal dispersion control of D'Appolitos is in fact a good thing, as it is for tall ESL's.

Generally speaking, the more controlled dispersion of a speaker the less acoustic treatments a room will require. 

Further, you literally can't have a point source if you are deliberately changing the dispersion on one or the other axis.

I came full circle back to kef and i'm not sure if it's because of my familiarity with the house sound or because they just due midrange better. I had the r105/3 and consistently listened at 104db peaks and the louder they played the more realistic they sounded. I was always let down by the bass which measured good in room but just didn't sound full bodied. I would say the benefits of the kef design is fairly easy placement to get most of what the speakers are capable of, most will be under powered, but many speakers that design for a flat in room response sound bass shy and take time to adjust to. Kef Blades have ironed out the midrange driver reflections making for a softer and more detailed treble play back than earlier designs and bass has been addressed.

I had Tannoy 10" Red's and Altec 604-8G's in refrigerators.  I couldn't cotton to either.  Then I landed a pair of JBL Hartsfields 15 years ago.  They are my forever speakers.  I love the 375 compression driver through a horn!  I also love my Quad 57's and LS3/5a's~

One sound quality I rarely see mentioned is how a speaker sounds all around the room. While the "listening" position is important, I also demand that speakers sound good as I walk around the room, and also around the house. I’ve had multi-way speakers whose sound falls apart as soon as you stand up.

My 15" Tannoy’s fill the room, and sound natural all around the room, and while I’m working in the kitchen. This is very important to me. I also use an 8" Tannoy driver as a center channel (in a DIY cab). It makes an ideal center, with no off-axis "phaseyness". No my Tannoys are not perfect, but this is a quality that they excel at, over non-concentric speakers.