This type of question is so room dependant, it is hard to offer specifics. But in general, I like to start with the speakers about 8' apart and the listening position about 8' from the plane of the speakers. BRM suggests 9' and that would be just fine.
The speakers have excellent off-axis response and need no toe-in. But if you toe them in slightly, imaging will improve slightly. Continue to toe them in and the soundstage will begin to collapse. Toe-in is basically a trade-off between a larger soundstage and more precise imaging. Each person will find his own optimum setting in this regard.
In regard to location with respect to room boundaries, there are two things to consider. If you get too close to the rear wall, the bass will tend to get more "boomy." Pull them out more, and the bass will be more accurate. At 18", you should be OK, but you might try pulling them out a little more and see what you think.
The second issue with placement close to room boundaries is impacted by the nature of human hearing. When sound leaves a speaker, it propagates in all directions. Some of this sound will reflect off of room boundaries (rear wall, side walls, ceiling and floor) and will be directed toward the listening position. This reflected sound will arrive later than the sound coming directly from the speakers.
If the time differential between the direct and reflected sound is long, your sense of hearing will interpret the reflected sound as room reverb. If the time differential is short, your hearing will interpret it as coming from the source. In this case, the image is "smeared" since the reflections are not in phase with the direct sound.
Obviously, the farther speakers are from the room boundaries, the later these reflected sounds will arrive at the listening position. It has been estimated that any reflection off of a surface 4' from the speaker will be interpreted as room reverb. Unfortunately, in many (if not most) cases, there is no possibility of positioning speakers this far from room boundaries.
I should point out here that there isn't much any speaker designer can do to deal with this situation.
Fortunately, there is a simple solution - room treatments. If you can install acoustic panels at the first reflection points, they will absorb these problematic reflections effectively killing these early reflections.
How do you know where these first reflection points are? Easy. (The angle of incidence equals the angle of reflection.) While seated in the listening position, have someone slide a mirror along the wall surface of interest. When you can see the speaker in the mirror, that is the point at which reflected sound will be directed toward the listening position. An acoustic panel in this location will help kill the reflection and (dramatically in some cases) improve sound quality.
Acoustic panels are often a WAF issue. Some companies like GIK have tried to address this by offering designs that appear to be paintings or photographs. Some companies may even offer the opportunity to use your own photos on the acoustic panels.
Acoustic room treatments are often the lowest cost, highest return items you will have at your disposal in terms of increasing sound quality. And they are often the only solution available to deal with early reflections (second and third reflections are not an issue because the time differential is great enough so that your hearing will interpret them as room reverb).
I hope this helps.
- Jim
