I have the SoundLab A3-PX speaker and have been
experimenting with speaker positioning and front wall (behind the speaker)
acoustical treatment options for the past year.
Assuming your speaker is similar to mine here are my insights:
* Speaker to Speaker Distance - as my room is only 135" wide I have my speakers quite close to the side walls with the distance between speaker centre points being 90". Given the large speaker size they can stand to be relatively far apart so start with them being 8' apart and try larger/smaller distances. Keep in mind that if the speakers are close to side walls that the concave rear firing sound will tend to fire into the side wall and room corner which will likely smear musical details, so to compensate you'll have to pull them out from the front wall about 6'(73") and have them firing straight ahead or with just a small amount of toe-in. Try and avoid directly firing into a room corner because untreated it sounds bad and treated with absorption it kills the "aliveness" of the rear wave and total presentation in my opinion.
* Speaker to Front Wall Distance - as a minimum you should aim for a 10 milisecond delay from the back of the speaker so that the rear reflection is not perceived as a separate auditory event from the front firing wave, and that its loudness can be matched with the forward firing wave. 10 miliseconds means having your speakers out from the front wall about 73.5" (1225*0.01) / 2 = 6.125' or 73.5" I've tried larger distances but the greater time delay of the rear firing wave created an echoey kind of sound. When shorter distances were used, the sound stage depth collapsed and phase issues seem to arise smearing musical details or shifting image specificity.
* Speaker Toe-In - If your sitting distance can be 1.5x times your speaker to speaker distance then try no toe in or very little. Nearer field sitting will of course require more toe-in. To each their own.
* Speaker to Listening Position Distance - SoundLab recommends a 1.5 - 2x sitting distance so this really depends on your room length as your main constraint.
* Front Wall Acoustical Treatments - Absorption kills the rear wave and changes the speaker's sound to one of giant headphones which is also not as loud because you're not getting any loudness from the rear wave (but you can turn up the vol control). The focal point of the convex rear speaker shape is about 3' so you can try standing diffusion up about a foot behind the focal point to see if you like the effect. My preference is to embrace the rear waves and let them reflect off of a wooden front wall (I covered the front wall with 8'*4' oak planks which sound better than drywall reflections - more alive sounding) but with absorption on the side wall that's behind the speakers to kill slap echoes. I have diffusion mid front wall. In short, the less treatment on the front wall the more alive sounding it becomes which is better to me than the headphone effect when thick absorption is used.
* Side Wall Treatments - with my speakers projection sound in a 20degree arc there is the need to treat 1st side wall reflections to smoothen out the freq curve (I use a Dayton Audio OmniMic for acoustical measurements). I use absorption at the 1st reflection points.
* Rear Wall Treatments - rear wall should be a mix of thick bass trap absorption and diffusion in front of it. Make sure that you're not sitting too close to the diffusion though. I use two rows of 7" thick GIK Monster bass traps with an air space between the back wall and the first row and between the two rows, and 4 GIK TriTraps fitted together in the shape of a rectangle that the second row of Monster traps stand atop. I also use 7-8 RPG Skyline diffusers that are also 7" thick in front of the bass traps.
Hope this is mildly helpful