Speakers with no rear wall, better or worse sound?

My current speakers are Avalon Opus with all Spectral electronics (DMA-250 amp/ 30SS pre). I am currently considering Magico speakers for which I would be willing and eager to optimize the room. I had a reputable dealer indicate that one needs a wall behind the speakers, albeit 4-5 feet back. I felt that having essentially no wall behind the speakers (i.e. no chance for reflected sound mixing with direct) would be preferred; but I am not the expert. I have pretty good imaging and excellent soundstage depth (width is reasonable). I have carefully consider first (side) wall reflections, floor reflection, etc. in the placement of the speakers.

The 'body' component is I believe the strongest supporting argument for having a rear wall. Of course we have the floor, side walls, and ceiling for some level of body. I was wondering if a good recording is to accurately reproduce a 'live' sound, it should also include the recorded characteristics of the room or recording studio. Mixing in different listening room characteristics adds some coloration (which may be desirable), but it is not accurate reproduction. I do realize that a completely dead room lacking no 'body' can lead to an equally dead or flat sound. One may say "whatever sounds great to you is fine." I would usually agree with this. My point in this thread is that it is impractical to (reversibly) add or subtract walls to find a preferred listening character. Fundamentals of acoustics/physics must play a role in understanding and addressing the limitations of any room that has not been purpose built for listening.

So I guess another angle on the original question would be: if you could change your room dimensions or characteristics to improve the sound, what would you do...no rear wall or putting in a rear wall.

Ablang

I really can identify with your situation which sounds quite similar to my set up. We also have a double door opening (French doors removed) 3 feet behind the speakers with about a 3 foot wall section flanking the double doorway opening on either side. There is another room behind the speakers with the back wall mostly glass. The depth of the soundstage is way back into the second room and bass is not all that bad to my ears. I have been speculating that the combination of a partial wall with the large double door opening and lengthy distance to the rear wall might be an 'ideal' mix of minimizing reflected sound behind the speakers without losing too much 'body' or room ambiance.

Thanks to all for the insightful suggestions. At a minimum, I have a few other considerations that do not involve major construction. I do not believe that bass in the current set up is lacking, so building a new wall may mess things up with respect to null and re-enforced modes as suggested by Josh358. Also, for Vicdamone (PS. I have a couple of records of the 'original' Vic Damone) I have spent countless hours playing with toe-in with my Avalons and with great benefit. I used to be disappointed in the soundstage width, in particular, which is currently much improved from all of the tweaking.