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

I can move the speakers about a foot farther apart or closer together, and I can change their toe-in. What changes, if any, might I be expecting or hope to achieve moving the speakers within these limited parameters? Could the sound-stage be affected? I’m not sure what the sound-stage should be like anyway. Should it extend to the left or right outside the speakers, or be mainly between the speakers?

Two things to keep in mind: speaker placement for imaging is almost entirely about absolute symmetry. You want to sit exactly the same distance from left and right, and with exactly the same amount of toe in. That’s one thing. The other one is tone. Big flat surfaces (walls, floors) tend to reinforce lower frequencies.

So what you do first is don’t worry about imaging but just listen for the bass and lower midrange balance. Try them closer, try them farther apart. You will probably notice a difference, even within the tiny range you have to work with. Leave them wherever you like the bass balance best.

Next take wherever they are and tweak and measure to get them symmetrical- equidistant, and also equally toed in. Listen for a solid center image, but also pay attention to the whole presentation, how deep and wide it is.

Now if you toe them in to where they are pointed straight at you the sound stage will be very solid, especially the center. Toed out and the stage will be more spacious, but probably not as solid. Make small adjustments in and out until you find the balance you like. There is no right or wrong. Its all about what you like.

The one thing you do want to be very careful about when doing this is perfect symmetry. Check carefully that they are toed in the same amount on each side. Even a small difference will result in a weaker image and if that is what you want then fine. But you do not want to be going for a holographic sound stage and then blow it with speakers all cock-eyed, and by cock-eyed I mean not inches but tiny fractions like 1/8". 

This is just the merest beginning, and focused on imaging because that’s what you asked about. But toe in also affects frequency balance, as most speakers sound a bit different off-axis than on. So you’re listening for that as well. But that’s why you go back and forth, take your time, play different music, tweak, listen, tweak, listen. 

Eventually you will find where you like them best. Then you can move on to putting them on cones, tweaking the room (if you’re able) or equipment (not only acoustic panels are acoustic, you know) and cables. Tweaking and fine tuning, there is no end. But this is the way to start.

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.