Nice work! Remember that you can only make one location sound the best in a room. There will always be low-freq pressure areas at boundaries (walls/floor/ceiling). You are using velocity absorbers and I would suspect more than 10 will be needed to create a nice response at the listening position.
You should definitly use the structured listening test (as described by Jesco) to find the best listening position - even a few inches forward or back will be noticeable. I use
Online Tone Generator with sweep tones from 30 Hz up to 200 Hz and watch the freq readout. Do this sweep at few locations forward and behind the ideal location (starting around 38% from the front wall). I make a chart and mark high and low SPL freqs at four or five locations and then you can visualize the most flat location from your notes.
6" panels straddling the corners like you have made should help down to at least 80Hz and sometimes lower.
You probably have a notch from SBIR (front wall to speaker baffle distance) around 190 Hz that could be fixed with some 6" panels on your front wall between your corner traps. Sidewall treatment will help with first reflection and L-R axial mode. Ceiling cloud with first reflection and floor-ceiling axial mode. I would recommend at least 8" for the ceiling cloud as your floor-ceiling mode will be around 70 Hz. Space couplers above the mix position can help with that, too.
If you plan membrane/pressure absorbers, I recommend a "shotgun" approach. Say you want to target 70 Hz. You should build three sets of absorbers, targeting 60, 70, and 80 Hz. Building a resonator that hits your target frequency is very tricky and spreading your frequency coverage this way all but ensures you will hit your mark. I recommend panel traps with 1/4" (6mm) plywood facing. Cut the plywood into half-sheets and make the panels 2 feet by 4 feet or 8 feet. Make 2 absorbers for each frequency and you'll have six absorbers.
Acoustic treatment can be iterative, so build a few devices and them measure to see the change. Then build more as needed. In small rooms, I rarely use diffusion and also rarely need tuned pressure absorbers.
best wishes!
Adam