What affects front to back depth in room/ system?

Try playing Moon River by Jacintha to get a perspective of image placement and over all system sound.  

Your perception of depth of soundstage is most likely negatively impacted by the first reflections (side walls, ceiling). Also, adding bass traps will help solidify the soundstage. When your brain needs to process sounds bouncing off every reflective surface, it will have a tough time realizing the stereo image. 
Easy way to test it is at very low volume where the reflections are minimal, does the depth increase?

Let's consider some of the basics of perceived soundstage depth.  Sounds that seem way behind the speakers have reverberation which is either natural--from distant-miking--or artificial.  Sounds that emanate from the plane of the speakers are typically close-miked without much reverb.  To have sounds in front of the speakers in a stereo system would require that the phase was reversed.  Or maybe it can be done with a surround system.

With regard to southern California dealers, I thought Alma Audio in San Diego did a nice job of setting up their Boenicke W8 speakers to create a sense of depth. The sound was very enveloping. Nice looking speakers that sound excellent, imo.