In my HT room, my subs were placed right besides the L/R speakers. It made placement of the L/R speakers hard, as it was taking up the entire wall, so I stacked both subs in the corner. To my surprise, the bass opened up, and was deeper. I had to turn both sun down. Not sure if it was the stacking, or placing them in the corner. For my room it works. As a bonus my L/R speakers are in a much better position.
Yes, bass is suppose to not be directional, and it moves faster through a solid object. Starting to think all the rules are changing with digital, and room correction. My 2ch system follows all the old rules and that works for it.