I never really experimented with where the ideal placement for speakers and sub would be. I have a wall to wall book shelf/entertainment center 6.5' high on the front wall. The main speakers are small DIY bookshelf designs that sit atop the outer book cases, angling down and in towards the listening area. My listening is about halfway split between settling into the chair at the ideal position, or working in the adjoining kitchen. I aim the speakers to focus on a point splitting the two positions.
The subwoofer was always right next to the sofa on the side wall. The sofa was centered on the wall, and the sub was immediately adjacent, acting as a side table. When the 1000 watt plate amp from Parts Express blew out for the second time, I found a very old 10 watt Sansui receiver for $4 at a thrift store. To see if the thing even worked, the easyest way was to hook the subwoofer up to it.
The first listen of the sub through the Sansui produced barely audible thumping. Nothing tuneful or impressive. I was about to disconnect and relegate the Sansui to bedroom computer duties, when for kicks I decided to try moving the sub around. I moved it to a point 14" from the wall to the back of te sub and then 28" from the side of the sub to the face of the book case..
Damn Son!!! Even with only 10 watts I was now hearing the deepest, clearest, and highly tuneful bass I ever heard inmy house. Obviously the 10 watts could not handle demanding bass or LFE passages, but I was sold on the importance of speaker positioning. Now I have a mighty 20 watt receiver that cost a whole $7, and I actually find myself turning the volume down to the sub on certain recordings.