Below are two copies of discusions I've been involved in regarding setting up my Dunlavy IVa speakers. Please do not under estimate how sensitive these are to placement and how long it takes to get perfect. If you have more questions first click on my posts, if you wish please feel free to e-mail me.
I began my placement process by following the 1/3 or 1/5 rule. I started with the speakers 1/3 of the length of my room from the wall in front of me. I then took 1/3 off that dimension to determine the distance from the sidewall. This is a rough starting point as determined by one of a few rule of thumbs. I use the Stereophile test disk #2 and the XLO test & burn in disk which have a series of speaker placement tracks. The first thing I tried was using a white noise (full spectrum) track and walked around my room to locate the amplified and dead nodes. If my seating area (1/3 into the room) coincides (which it did) with these nodes I knew I must change my starting point. I moved the speakers ½" at a time in a diagonal to keep the relationship from the walls. Once I had a rough location with no node problems I tried an out of phase mono recording from the XLO disk. The sound should appear to come from all directions with no discernable source. This proved to be an invaluable track on the XLO disk. I worked this and the white noise tracks back and forth until I again had both working. I then used an in-phase mono track to work on pinpointing (toe-in) the sound to a very small point location. These were my start points, there are a number of other tests which are helpful, but these were my major tests. It was now time to listen to some familiar music. I find female vocal jazz quartets to be excellent tools. The voice should appear to be centered (if recorded centered) and stay in the center as I move side to side and front and back. If the voice is too large, not sounding like it came from a mouth then I'd toe the speakers in. If the spot was too tight I'd toe out more. To get the spot to remain centered I moved my listening spot for and aft until it became very stable. Now using a disk with more instruments I could look at sound stage width. The stage should be as wide as possible without losing my center spot location. Back to the jazz vocal I now look for depth. The drum and bass should appear behind the singer. The horns should have a defined point with space in front and behind it. If this depth does not appear (like mine) I tried moving the speakers forward or back ever so slightly. There is a magic spot that the speakers work with the room to bring it all together. The last thing I look for is bass definition. Again I found forward and back impacted bass. A stand up bass should have a definite location, and the note made from the pluck of the string should appear well defined, almost like a round spot. This needs to remain focused down to the lowest notes. If your not dialed in the note will appear to flatten out, and if real bad it will stretch across your floor. These speaker movements were tinny for me in the end. I'm talking 1/16" and the focus would clear up. (That's after a lot of time to get real close) The entire process took about four hours the first time. I listened for a week and reworked it four or five times. It helps to enlist a friend with good ears who is not so close to the process, mine was very important in the final sessions. Once we were sure of our location, we measured the speakers back and side corners to the wall, it turned out one speaker was slightly off of the other. Once we re-aligned them to be exactly the same, one last toe-in and it was indeed there.
So what do I hear now? Every instrument is easy to locate, even when there are 10-15 instruments. They appear within there own space, with room in front, back and on it's sides. When it's well tuned this should not be a stain to hear, but simply the way it is. The center image is tight ( in a realistic way) and does not move from the center. The stage appears to extend well beyond my speakers, but not so far as to lose the center image. The entire presentation comes alive, as if it's in your room, it took a long time but it is extremely natural and not a strain to find all the instruments on stage. I think it's just trial and error, just keep playing. My friend and I tried to better the sound by starting over once and the speakers ended up within an 1/6" of where they started, just a bit further back. I kind of think there is a spot they belong, and if it's the right one you'll find it again. Some of these features my have had as much to do with the tweaks I've made as did speaker location, I believe they do work hand and hand. I just started a post on the tweaks I did this year, it's titled "the winters lessons". Above all, have fun with it, it's not a race.
The rule of thumb is 1/3 into the room. If that doesn't work for your room 1/5 is the next best. Your seating position also should follow that rule. If this doesn't work for seating, Lugnut's comment of "experiment with absorption behind the listening position" is what you will need if you end up 1/5 or right at the wall as recommended by Audio Physics and Dunlavy. At any rate a min. of 8' and better at 10' between your ear and the tweeter.
The problem you may find in your room is that at 1/5 the depth will suffer, you may need acoustics on the speaker wall to help this.
BTW, I'm set up on the long wall, 1/5 for the speakers and 1/3 for my ears.