The first thing that might be helpful to understand is that lower bass frequencies are omni-directional and don't function at all like higher frequencies. Here is a succinct article that may be helpful there:
http://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1
What others are getting at is that there's no way to know what the best placement for a sub is in a given room. Even if they had all your room dimensions they could only make an educated guess since there are so many variable. I've heard other members mention the "Murphy's law of subwoofer placement," the idea being that where a sub looks best is rarely where it sounds best. So you could do the subwoofer crawl (Google it) or simply move the sub around to different places till you find what sounds best to you. (Be sure to rerun Audyssey after each change.) If you really get into it you could download Room EQ Wizard (a free program) and a buy a USB calibration mic (< $100). This would allow you to measure the frequency response at your main listening position with the sub in each location.