Could be the headrest on your chair that is changing the sound also. I've noticed a difference in sound based on reflections off the headrest; thats why I got a saw and cut mine off (headrest, not head).
Vandersteen's are very picky about proper placement. When I had mine I found the set up guide on line and followed that. It was some sort of mathematical equation (maybe someone can chime in here...). It was pretty specific on the distance from the rear wall, side walls and listening chair. Vandersteens bass response is also effected by the toe, as toe changes the angle at which the bass reflects of the rear wall. Also, they sound best bi wired. I noticed that they sounded better,in my case, by using a cheaper bi wire than a more expensive, better, single run.
Vandersteen's are very picky about proper placement. When I had mine I found the set up guide on line and followed that. It was some sort of mathematical equation (maybe someone can chime in here...). It was pretty specific on the distance from the rear wall, side walls and listening chair. Vandersteens bass response is also effected by the toe, as toe changes the angle at which the bass reflects of the rear wall. Also, they sound best bi wired. I noticed that they sounded better,in my case, by using a cheaper bi wire than a more expensive, better, single run.