Wow - that 30 page experiment with sub placement was sure impressive. The 50 subwoofer experiment, and then the 5000 sub experiment were kind of funny...
http://www.harman.com/wp/pdf/multsubs.pdf
It looks like their conclusion matches what you found. Thanks for the link...
"Two subwoofers, at apposing wall midpoints, performs very nearly as well as four at the midpoints and gives a much better LF factor"