This raises an important point about electrostatic speakers, as well as any other thin plane or cone speaker (such as the Linkwitz Orion) where the front and the back are open. All of these so called bi-pole speakers have that in common, as opposed to the more common mono-pole speakers that most of us have. They require careful room placement so the rear wave reflects off walls behind the speaker and arrives at the listener in phase with the front wave. These front and rear waves can complement each other, but it requires some trial & error in room placement before it works well. Although this can result in wonderful sound, they usually end up far enough away from walls to effectively dominate the room. In my opinion, that is the major downside of these speakers.
The speaker in that video mentioned that feature, but I don't think he made the point well enough. The bi-pole feature is, in my opinion, what allows these speakers to sound wonderful, but only if they are carefully located within the room.
