In my room I have all of my storage units even with the listening seat and behind along the rear wall for diffusion. I reserve the areas in front of me for absorbing acoustic energy to create those reflection free zones. I guess that comes out of the older school of thought for the LEDE room where you want things that way, absorptive in front and diffusive in the rear, but to a much greater extreme.
You had mentioned rear wall behind your speakers. Did you mean the front wall? If so, my personal opinion is not to have anything between your speakers up passed a certain height. That is an area I reserve for absorption and treat to eliminate reflections. However, I do know of some that prefer and do have tall equipment racks againts their front wall and swear by that placement.
Dave