I got your message on this, but also noticed the post you made here so I figured I'd let some others give their feedback first, and then I have been so busy getting ready for the show that I haven't gotten back to it yet.
Ideally you need to take some measurements to dial it in perfectly.
The number one error in measuring them is everyone tries to measure left and right speakers and subs at the same time. This just causes cancellation effects from different distances and time delays created by multiple sources. Just measure left speaker and left sub individually and then together to get the phase, crossover, and amplitude correct.
The damping settings will have an effect on imaging to some extent. Don't assume that high just means tighter or better control and thus better sound. You may get better sound on low damping if the extension filter is set low, and better imaging.
And don't get caught up in trying to measure distortion figures. Measuring or trying to take any distortion measurements outside of an anechoic chamber is futile. The actual distortion numbers will be at or below the room noise level. So true data will be covered over by the room noise levels.
I'd also like to comment on implementing the servo woofers. I tend to prefer the H or W frame design. I like the H frame best as it divides the side panels into smaller areas and maintains a larger opening. The W frame leaves a much larger panel area on the front side between the drivers and the side panels have to be increased to thicker material to compensate for the pressure created in that area.
I'm using 1.25" think material on my H frames and lined with No Rez to eliminate and control any panel flexing and resonances, and that is about what it takes.
Going to a Ripole design like the one pictured unnecessarily loads the drivers and causes the amp to use more power to maintain the linear output levels. So it eats into amp headroom. It also will limit the upper range quite a bit. But more importantly is that it allows for very large panel areas in front of each driver. To do away with panel flexing and resonances that this alignment will cause will require panel thickness in the 2.5" to 3" thick range. Most of the designs I have heard using this alignment and 3/4" plywood is what I'd call a buzz box. So I don't recommend it.