The droning you mention seems to suggest that your room modes are being strongly stimulated. You didn't say what part of the response band seemed most disagreeable. If it is mainly in the bass, these modes are related to the room's dimensions and speaker placement is important to minimise this unwanted effect.
If it's more mid range then possibly it is due to contribution from first reflections. Having your listening position up against a rear wall is one of the worst places, too, partly because the rearwards first reflections are near coincident in time and relative energy with the direct sound. Side wall reflections cause similar problems and are associated with image blurring plus comb filtering colouration, so adequate spacing or diffusion/scattering treatment can help a lot.
Placing speakers close to room boundaries puts them in the max pressure part of the room. Just to investigate the behaviour in your room, rather than try arbitrary positions, move them systematically until you know where gives the least droning. Think of your room as a test space while trying to solve your problem.Then you can put the speakers in the least bad place and consider room treatment to ameliorate remaining, less tractable problems.