There's not really a "horn action", just wave-guide. Neither in this EV column. However, a wave-guide probably smoothes out diffraction effects.
It's probably funny-looking on the back side;
Indeed. Traditionally, column speakers are wall-mounted, which also helps with the LF response, but today the trend is using these as an immersive source. The back radiation is what the performers get in guise of stage monitoring. My only experience with that was not very satisfying, but not as bad as litening to the back of a traditional point-source speaker.
The Bose Panaray litt is an interesting read, because the polar responses are very well documented (and typical of a column behaviour); it shows that standing behind a column at about 120° from the main-axis (which would be the typical position for a performer), the response is pretty decent up to 4-5 kHz, which is about all that's needed for stage monitoring.
The vertical directivity is expressed as a single figure (40°), which is meaningless. The directivity pattern narrows with frequency, but that's not all. The Bose litt shows openly the existence of very narrow lobes, which result in important timbre variations with the listener's ears position. Again, that is not big news since it's been predicted and known a long time ago; the fact that listeners enjoy column speakers is a testimony to the adaptability of the audition process.