Rear wall effect on sound stage location?

I have a large listening room (18W x 30D) with cathedral ceilings. My speakers are Vandy 2CEs placed 8ft. apart and 4ft. from the front wall. I sit about 9ft. in front of the speakers. I get a great wide and deep sound stage with vocalists/instruments that appear to be behind the front wall and slightly above the speakers. I am very pleased, with no complaints.

However, in many of my friends listening rooms with rear walls much closer to the listening area, the vocalists appear to be more even to the speakers or even in front. Does anyone know if the location varies with the closeness of the rear wall? Do earlier reflections pull the sound stage in? Where is the most desireable location?