Subwoofer placement is a complicated issue. I never advise using one sub. Two subs would ideally be placed in the corners with digital correction of the group delay. Without digital correction the subs are better off between the speakers against the wall with all speakers and subwoofers on the same radius from the listening position. This assumes that all the drivers are in phase with each other which may or may not be true. What you have within reason between the speakers does not affect the imaging at all. Some people are fooled by their visual perceptions. Just don't part a bus between your speakers.
Subwoofer between speakers?
After reading through a thread relating to the equipment rack between speakers, I assume that the sub between the speakers is also a no-no?
My speaker stands are 24.5" high, and my sub is 24" high, so I was thinking that the sub cabinet being below the mid-range driver might mitigate the detrimental effects to imaging. But I read a reply in the thread that I alluded to which talked about an amp between the speakers having a negative effect on imaging . . . therefore it stands to reason that a big bulky sub cabinet would be about 20 times worse.
I know that ideally I should experiment with placement . . . this is an extreme near-field listening room, and options are limited. I could get it to the outside of my right channel speaker . . . in theory, would that be better than in between?