Loudspeaker dispersion-

Both speakers work together to place images in space, between the speakers. Vertically, each speaker works by itself.

What are the speakers? Most panel speakers (e.g., electrostatics, planar magnetics) have very limited vertical dispersion, which is why they make them tall. Some speakers have wave guides that determine the dispersion pattern. A tightly spaced vertical array of speaker drivers (such as in a dynamic line source speaker) has very limited vertical dispersion.

D'Appolito (and most other) MTM arrays have a limited vertical dispersion as well. There's something about the tweeter with midranges both above and below that limits the vertical dispersion. In many cases limited vertical dispersion is intentional to minimize the sound bouncing from the floor and ceiling and smearing the image.

That's a good question!

My guess would be it has something to do with tweeter location on the front baffle and how sound is reflected off that accordingly.

Also possible that different soft dome designs have different internal dispersion patterns by design despite the outward symmetrical appearance of the dome.

Or both.