BFM's response to the same article*:
http://billfitzmaurice.info/forum/viewtopic.php?f=18&t=17476
*posted at http://www.synaudcon.com/site/author/pat-brown/how-boundaries-affect-loudspeakers/
Other reading- Rules for Subwoofer placement and stacking http://billfitzmaurice.info/forum/viewtopic.php?t=398