Well I only have tried the bass traps in that position with the Keesonic Kolts and ATCs. It seems to help by smoothing out the mid bass and gives the feeling of bringing the low bass up a bit, maybe by filtering out some peaks in the response and making it more even.
Soundstage seems very clean now, I have always had an 'issue' that the soundstage in my room compared to Scalford or Demos just seems confined to the speakers, now it sits in front and seems to extend further out to the sides too, not the most important thing but a nice change.