Adjusting speaker positioning. What, if anything, to expect?

Textbook Nearfield Listening Positions as described.
Try changing the distance between the Speakers.
The A3s are much larger than my stand-mounted mains.
Also the 15' vault should really help with A3s. 
My experience suggests closer would be right.
From 8' to 7' and leaving the listening position the same.
You should experience a sense of more power and greater depth.
As a goal anyway.
Before changing the spacing though do experiment with toe-in.
Go to zero toe-in (and any between) in the current position and listen for a bit.
Get an idea of what your sense of the sound is.
You may also experience some difference by moving the A3s toward the listening position.
Move the Sofa out of the way and Stand away from the back wall at an
equal distance to that of the Baffles from the front wall.
And listen for a bit.
The final positions could be inches in either direction (short axis/width).
But get a sense of what the sound does in the space.
Decouple the A3s if you have not done so and if the room is Lively / Bright (hard and harder surfaces) start thinking about treatment.
Once you have a good idea of how the Loudspeakers integrate then you can fine tune. 

Closer to the rear wall is going to reinforce bass response. You are pretty close, but mentioned that is your option. So be it. As mentioned, at the end of the day, it’s about personal preference. You mentioned you were not sure about sound stage and imaging. Sit in your selected position with your eyes closed, point to where you hear the main vocal track. A good vocal recording is helpful here. If you are pointing dead center and possibly slightly upward you are off to a good start. You speakers should be “invisible” to your ears. You should not be able to hear either speaker is a singular unit. Perhaps an instrument on one side or another, but not the speaker as a whole. To find your sweet spot, I suggest getting a chair on wheels and as MC said, put it equidistant to form a triangle. Then slowly move back and forth and see where your favorite position is. That way your head height remains consistent and relative to your final listening position. Mostly have fun with it. 

Thank you very much for the detailed explanation, Millercarbon. Would you mind clarifying some of the terminology you used so I can follow what you are saying carefully. What exactly do you mean by "imaging". I’ve heard the term used many times, but never had anything but a vague or loose understanding of what it means. Also when you refer to "bass and mid-range balance" what are you meaning? I’m only guessing, but Is it the amount of one in relation to the other, or something entirely different?

As you suggest, I will be careful to keep everything absolutely symmetrical to the 1/16" inch if need be. Thanks for pointing out the need to be that exact.The current set-up when you sit in the center of the couch is an equilateral triangle with the speakers 8’ apart on center and the listener eight feet from the front of either when seated. Does this sound like a reasonable arrangement? The speakers are toed out a bit from that, so I’ll toe them in as you mentioned so they are pointed directly at the listener’s head to have a solid center image to start with, and proceed from there.

There aren’t any big flat open surfaces to contend with, unless you count the vaulted ceiling, so that shouldn’t be an issue. The floors are oak, but the area in front of the couch and speakers is covered with a thick (Persian) rug the width of the couch.

One last question for you or anybody. How far should the sound stage extend beyond the speakers, if at all? I read somewhere on site the sound stage should not extend to the left or right of the left and right speakers unless they are wired out of phase. Is that so? The sound stage now often seems to emanate from inside the shelf area holding the components between and in back of the speakers.

Again, thank you,

Rego and geof, your posts came in while I was writing this response. I will get back to you in the morning as it is getting quite late and I have to call it quits for tonight.

Mike

Mike, Imaging is the ability of a system to recreate the location, size and depth of instruments and voices. It is what stereo is all about. Whether or not a system can do this well depends on the type of speaker and acoustical issues with the room including speaker placement. Dynamic speakers like yours radiate sound over a wide area creating rather loud early reflections off the side and front wall. Early reflected sound arrives at your ears just after the direct sound from the speaker blurring the image like an out of focus picture. This is the problem with the smaller rooms we tend to put our systems in. Late reflections like off the rear wall (other side of the room) are heard more as an echo. They are also much lower in volume. Late reflections do not blur the image and can make your room sound larger if the early reflections are controlled. Bass is another issue altogether. Anyway there are threads that discuss finding and controlling early reflections. Moving the speaker will change the location of these reflections. Moving  speakers like yours farther away from the walls diminishes early reflections and improves the image but decreases bass efficiency. This is a strong rational for using separate subwoofers and the reason many audiophiles keep their speakers so far out into the room. You can sort of have the best of both worlds if you keep the speakers right up against the wall and deaden the surrounding wall with acoustic tiles or panels. Millercarbon is an old school symmetrical guy and for speakers like yours I think he is correct although there are some like Roger Sanders that would argue with this. With speakers that are very directional like horns symmetry is not as important. My system set up is perfectly symmetrical because my brain won't tolerate it any other way. It also can't stand to see a crooked picture. My speakers are ESLs and they are also very directional. 
Anyway, when you move your speakers around pay close attention the image. Instruments and voices should be very distinct and float in space.
Close your eyes. It should sound like the band is right in front of you. 

As I oft counsel the method of moving speakers a little one way or the other and listening each time you move them is far from ideal and can only result in finding local maximum speaker positions, at best. You cannot find the absolute best positions for both speakers that way. The only way to find the absolute best positions for any speakers in any room, regardless of room treatments and regardless of the rest of the system, is to use the speaker set-up track on the XLO Test CD or similar test CD. It’s the out-of-phase track. When you get the most diffuse sound using the out-of-phase track you will get the most focused and correct sound when the system is in phase. Even as your system evolves the speaker set-up track can be used again to establish new best speaker positions. Trying to find the absolute best speaker positions by trial and error is like trying to solve x simultaneous equations in x + n unknowns.