I have seen comments similar to this before and, having some experience with the matter, offer this advice:
Although some sub cabinets will place a bookshelf speaker (or drums as made by nOhr) at the correct ear height for good imaging it is highly unlikely that the ideal speaker position and sub position will be the same i.e. a main speaker will normally sound the best a significant distance from the front and side walls (try the intersection of thirds as a starting point) while the subs will generally sound better (louder, smoother etc) when placed closer to the front corners. In summary; use high quality speaker stands and optimum placement for imaging and mid frequency response and load your low frequencies in the corner (in stereo) for deep bass and fine tune crossover points, position and sub volume for flatter overall frequency response.
