I have worked with one set of the original SC IV's ( not the re-designed "A" models ) a while back, another set of speakers* that are very similar in design but FAR more advanced and "tweaky" and several "good sized" speakers using MTM designs. As such, that experience is what i based my comments on.
Based on the experience mentioned above, I will only add that if one can't place the speakers along the long wall and minimize the amount of "clutter" between the speakers so that they can directly "communicate" from side to side, measurable toe-in will probably be a necessity. MTM speakers are designed to "spray" the sound out horizontally and if the speakers can't "blend in the middle" due to obstructions, one must force the situation by aiming them inwards to the point that the signals are forced to blend together.
Having said that, I'm sure that Felix' experience with the Dunlavy's that he owns is 100% accurate. I'm also quite sure that John Dunlavy knew his product well enough to know how they work best and included his thoughts in the speaker manual. The only variables to the two above situations are that room acoustics do differ, along with the constraints of various installations. This is not to mention that one can enjoy / prefer slightly different presentations from someone else using the same speakers. As such, one WILL have to experiment ( to a much greater extent ) with speaker placement when using a "less than conventional" speaker design in order to find out what works best for them in their room. I don't know of any speaker made that can be placed in one given set of positions, regardless of room layout or size, and obtain universally repeatable performance. Some basic suggestions may provide pretty consistent results, but there will always be exceptions to the rule due to the above mentioned variables. In other words, one size does NOT fit all. Sean
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* A custom built set of speakers using similar driver layout using as good or better quality drivers, far more advanced individual cabinetry for each driver, better quality internal wiring, no passive crossover components and active quad-amplification.