The thing I have found with difficult rooms is you can either invest in treatments and go to great length to fight the room that you have to live and listen in or you can adapt the strategy of letting the room work for you rather than against you.
My conclusion from having used both omnis, planars and conventional box designs in various shapes and sizes of rooms over the years is that omnis will fill the room with sound more evenly and with greater ease for you in assymetrical rooms than more directional designs.
Thats not to say that placement doesn't matter with omnis because it does, but omnis just tend to work with the room more naturally than do more directional designs.
The OHms are acatually not completely omni, the top is covered by a more conventional wide dispersion soft dome tweeter angled inwards 45 degrees, which helps retain the naturally wide soundstage of the omni Walsh driver that covers the rest.
The soundstage almost always naturally extends completely to the side walls both left and right even if the speakers are placed more closely together and located either significantly right or left of center.
Toeing the OHMs outward to point the tweeter more directly towards the listening position can be used to reduce the width of the natural wide soundstage if needed. When properly set up a couple or few feet from the rear wall, the sound stage will also typically extend back well beyond the rear wall on good recordings.
