There is not much difference in Omega and Amphi except the size. I am giving you experiences of the German distributor who along with the US distro has been the longest distributor of the Analysis.
I owned the Summits - more of an hybrid than a planar, and had the Omegas in my room for audition.
That said, listening to multiple speakers in multiple rooms, and piggybacking on another's experience curve always adds more to the learning than referring to our own systems experiences.
Also, if Lissnr says the Diva did not work in his 18*13 room, I would listen.
It might also be that you listen more to chamber, I listen more to orchestral.
Well, actually I listen to orchestral quite a bit, perhaps not as much as chamber but plenty I would say. I am particularly fond of violin and piano concertos rather than actual symphonies...although I like those too.
As for planars, not only have I owned several, my friends have had many many planars. I personally have had the following: AudioStatic ES100, Infiinty IRS Beta, STAX ELS F-81, Apogee Caliper Signature, Acoustat 1+1, Acoustat Spectra 2200, DIY planar hybrid with BG driver and Acoustat Spectra 4400. My friends have had the following: Acoustat Spectra 22, Acoustat 1+1, Apogee Studio Grand, Apogee Stage, Apogee Diva, Apogee Scintilla, Apogee Fullrange, Apogee Grand, Apogee Centaur Major, Quad ESL-57, Magnepan 2.5r, Magnepan 1.6QR, Magnepan 3.6, VMPS 30 (planar hybrid), Relco Sinus One, Final 1.4 reference. I have heard them with all kinds of amps: hybrids, SS, PP tubes and SET.
I have heard them in large and small rooms. Divas in large and smallish rooms. They worked fine in a smallish room. Acoustat Spectras work great in small rooms, as do the Apogees I have heard. In big rooms it is more hit and miss because there is actually far more room interaction as you typically sit further away and there is greater delay in the reflections. The nature of dipole means that you have nulls at the sides of the speakers and this minimizes the first reflection interaction with the side walls. If it is a tall line source then you have much less interaction with the floor and ceiling as well because there is very little dispersion vertically.
I had my planars always a little bit over 1 meter from the front wall but they could be very close to the side walls without having a significant impact on imaging and soundstaging. I got fantastic imaging and soundstaging with my Acoustats even though one was only 10 cm from a side wall and the other was open to and L-shaped part of the room. Shouldn't work, right? But without that first reflection the imaging didn't get skewed. Ask Christoph about how it sounded. It is the main reason he has Acoustat Spectra 22s (same as 2200 just cosmetics) and KR VA350 upstairs. You do have to toe the speakers slightly and maybe people are having issues that can be solved with how they set up the speakers.
With my horns, I have them in a room that is small and in theory shouldn't work well...but I have toed them in radically to minimize the side wall reflections and the imaging is very good. When I had them straight ahead it didn't work well at all.