No doubt you've heard of the rule of thirds. This rule and the 29% rule are discussed in the section called "monitors" in the article below.

Admittedly I don't have the 2' minimum to my back wall as described in the article. I only have 16". I've had to trim my bass by 6dB as a result. The Pioneer does not have bass management so I can't use a sub to solve this. I may continue to experiment by moving the speakers closer to each other and then moving my MLP closer to increase my distance to the back wall as the article suggests. That may negatively affect the holography though.

I'm also considering removing the wall.

http://www.barrydiamentaudio.com/monitoring.htm

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated