Room Treatment? How important is it to treat the wall behind/between the speakers?

@macg19  Thanks for taking the time/effort to take measurements with DIRAC. 

It appears that DIRAC is working as it's expected matching L and R speaker decibels levels as best it can based on whatever parameter limits you set.  But you're on step 4 when steps 1-3 aren't quite finished.  There is a sequence to treating a room and it generally goes like this: (1) begin with Early Reflections and L/R speaker's reflection symmetry within 0-10ms which usually involves 1st order reflections in most domestic sized rooms.  Energy Time Curve data is used for this step which REW provides but I don't know if DIRAC provides.  (2) Bass Decay time should be dealt with next to reduce masking of midrange details when bass decay times are excessive compared to those of mids/highs.  A T30 metric is found within REW and you can get pretty granular by using 1/3rd octave intervals to see where problems lie and what the best type of bass trap is to use (velocity or pressure). Again, not sure DIRAC measures this as it was designed more for frequency response and not the time domain (i.e. early reflections and decay times). (3) Mid/High decay times come next with the use of diffusion and reflection and appropriate T30 decay times suitable for your room size. (4) last comes frequency response and gentle EQ which is where DIRAC lives as I understand it. (I use Audiolense XO for FIR convolution filter creation myself.)  While Frequency Response is usually the default go-to chart to use, it is impacted by the sound bouncing off reflective surfaces between the speaker plane and your listening position.  Because the frequency response's informational content includes the effects of early reflections, it's important to get those locked down first otherwise you're chasing your tail.  Looking at your system picture I am not convinced that the wooden slats on the left sidewall and curtains on the right side are giving you symmetrical early reflected energy especially in the 1 and 2kHz octave regions where our hearing is most sensitive - the wooden slats would preserve the 1 / 2kHz octave energy while the drapes would attenuate it, and I hazard to guess that only through the use of DIRAC are the L/R frequency response curves very similar.  I'd encourage you to try the same type and thickness of absorption panel on each sidewall as a common denominator to different construction materials used for each sidewall which impacts tonal balance.  Play with absorption panel angles and distances from the wall behind it to achieve L/R Early Reflection symmetry before turning on DIRAC.

Reading your DIRAC graph:
> first off, the chart looks like it might be at 1/24th smoothing which shows all the nasty bits, so don't be surprised or discouraged. 
> the curves track each other nicely which is DIRAC's sweet spot but range from about -2 to +8dB for a +-5dB range which should ideally be at +-3dB or better.  Getting the sidewall's 1st order reflections symmetrical should help DIRAC out so that it doesn't boost/cut EQ as much.
> The large "U" shape in the 30 - 80Hz range is trouble as a kick drum lives in the 40-70Hz range as does bass guitar, and other instruments.  The R speaker at 45Hz is about 6dB louder than the L channel - not good. This could be caused by the R speaker being near an external wall with brick/concrete behind the drywall which reinforces these low frequency's energy whereas the L speaker is near an inside wall that is less stiff and flexes. Pressure traps can help here like GIK Scopus T40 / T70 traps as can multiple subwoofers.  Experiment further with speaker / chair positioning to see if that "U" hole can be remedied as it is beyond DIRAC's boosting limits.

@macg19   https://pmamagazine.org/early-reflections-101-the-first-10-milliseconds-that-make-or-break-stereo-imaging/

@macg19   Sure, I can do the analysis for you.  Let's communicate via PM so that you can tell me what you're after and I can advise you on which measurements to take, how to take them, what file format to send to me and I can return a custom Report with additional charts and analysis that REW doesn't provide, including type and placement of treatment recommendations.  Send me a PM if interested.

@macg19 Congrats on a nice looking rig and room.  If you're open minded to a few suggestions for better sound, here goes . . .  these are not criticisms just ideas to try out.
> Early Reflection Symmetry: (1) I'd pull your speakers forward so that your soundstage depth may improve but also the carpet now catches the speaker's 1st order floor reflections. (2) Is the ceiling treated? Might you consider white colored Skyline diffusers made from Styrofoam at the 1st order reflection points so that they blend into the ceiling color wise and so that you aren't impaled should they fall? (3) Sidewalls are different construction materials and may cause havoc with tonal balance and imaging - try a stand alone 6" thick GIK Monster bass trap for each speaker's closest sidewall.  The right stand alone trap should be the same distance from the right speaker as the left stand alone panel is from the left speaker.  The farthest speaker's sidewall 1st order reflection (R_speaker -> L_sidewall and vice versa) may require asymmetrical treatment as pulling the speakers forward may now place the right speaker firing into the left doorway (essentially an absorber) so you may need to experiment with just a right sidewall treatment of another stand alone absorbing panel by the bay window for the left speaker's 1st order reflection or a reflective 3/4" thick reflective board to redirect away from you to acoustically mimic what the left doorway is to the right speaker.  (4) Place 1D QRD panels centered on the front wall and front wall corner bass traps
> have you access to acoustic measurement software (REW / OmniMic)? If so, then Energy Time Curve data for early reflections will help with trying to achieve acoustical L/R symmetry for 0-10ms.  I'd suggest frequency limiting the ETC data to 3 one-octave ranges centered at 500 / 1 / 2kHz as their reflection energy differs based on wavelength, speaker directivity, toe-in angle etc.  Focus on the 500Hz and 2kHz octaves for L/R cross-channel symmetry for tonal balance and imaging respectively.  You should also try to achieve cross-octave symmetry across the 3 octaves (500<->2kHz) for each channel separately for tonal balance purposes.

@macg19   Kudos on all the effort and combinations and permutations of treatment placement!!!  Lots of move->listen->measure cycles I’m sure.

Just a note about the 4 Sound Blocks not seemingly made any difference to the DIRAC frequency response measurement (with the 1 exception that looked ridiculous), for peaks/nulls below about 100Hz you’re better off using GIK Scopus T100/T70/T40 membrane traps and several of them as they’re just 2’ x 2’ in size (depth varies) - the Scopus T40 and T70 should improve your 59-60Hz woes when placed against a wall that has an exterior brick/block/concrete backing behind the drywall, in other words exterior wall, and also when placed near the sound source (speakers, sub)..  On the other hand, the Sound Blocks likely affected (reduced) the decay times of the frequencies they affect which REW’s RT60 decay time chart (but look at the T30 metric, or Waterfall chart ) would show and which DIRAC won’t show.  If your mids/highs are being absorbed by the curtains on the right sidewall, then equal absorption on the left sidewall should provide the L/R symmetry you seek.  Another way to approach it is to use an angled board on the left sidewall to redirect the reflections past your head to mimic the absorption the curtains provide.