Are you sure it is not interfearing with the TV picture being only 1 foot away? If you have 1 sub, then up front somewhere could "generally" be a good option (I would place a second sub in the back to balance bass in the room). You will have to experiment. It has been said that if you place the sub in the listening position and walk around the room looking for the point of strongest bass, then that is the optimum placement. This may not be practical though, having a sub in the middle of you space. A corner placement will boost the bass the most. If you do place it up front, try it using both phase settings to see which yields maximum bass.
orangeman
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Corner loading *may* yield the loudest bass at certain frequencies but it is almost never the proper placement for smoothest response. Corner placement guarantees a serious hump. In my case the hump is at 44hz. Placement at the halway point along a wall will (usually) yield the smoothest bass response over its operating frequency and will minimize humps.