Some good info and tools about speaker placement:
 
Read this in tape op a while ago:
http://tapeop.com/tutorials/78/monitor-positioning/
 
These are on the author's website:
http://www.carltatzdesign.com/acoustic-tools.html
http://www.carltatzdesign.com/acoustic-tools/axial-mode-calc-example.pdf
http://www.carltatzdesign.com/acoustic-tools/the-null-positioning-ensemble.pdf
 
 

That is all good info.  I've done all of that, AND the way I position myself correctly with my head in front of the apex of the speakers is I have little mirrors on my speakers, so I position myself so that I can see my eyes in both mirrors, then move forward until I'm 18" in front of that position (moving a total of about 22" to account for the distance between my eyes and ears).
 
the mirrors also help me set the acoustic center of the speakers with my ears.

Beagle, the mirrors on your speakers is an interesting idea. Might have to try that. Thanks!  
 
And thanks for sharing, RJ!