i have always set my subs up to be adjacent to the mains - i am more interested in soundstaging, and a smooth frequency response, than trying to get the subs "coupled" to the room for max bass boost. i now use a deqx to get this; before the deqx, i used an active x-over to cross the subs to the mains, & dialed it all in w/a pink noise generator & equalizer to measure for the flattest response... you can then always tweak the output of the amps driving the subs a little, if you want more low end on some music, or for general listening. at least this way, the basic smoothness & soundstaging will remain...
ymmv,
doug s.