200Hz is localizable, but only to the extent determined by ITD. Therefore any point on a circle, whose plane is perpendicular to a line drawn through our ears, is indistinguishable from any other point on the circle.
In other words, you can chop off your outer ears for midbass frequencies. What, then, distinguishes "front" from "back"? Besides your eyes, of course

At 200Hz, you can only localize based on ITD. So ... if the driver location "behind" you generates the same ITD as the driver location "in front" of you, you have no hearing mechanism to distinguish one from the other.
In still other words, all places "behind" you are not equally good ... just as all places "in front" of you are not equally good. It is true that a midbass driver
directly behind your head is indistinguishable from a midbass driver
directly in front of your head ... but a midbass
directly in front of your head is not optimum for stage width
All of these points become obvious by simply understanding ITD, and the simple geometry of a circle
In practise, the illusion is ruined by driver distortion, or panel vibrations, generating frequencies higher than you intend ...
edit : and this whole argument is
completely separate from a "rear fill" discussion, which revolves around delayed, perhaps L-R processed, higher-bandwidth drivers located behind you in the ambient field.