My GPS receiver is located in the same place. I am not really bothered by any variation in my actual location as opposed to my location on the map.
I don't think many of the commercial GPS receivers are accurate much lower than a couple meters anyway. The distance from the front windsheild to your back window can't be any more than 2 meters or so. To me, being off by a couple meters is insignificant seeing as vehicles are roughly 4/5 meters in length.
If anything, I'd look in your software preferences or configuration to see if there is a way to adjust an offset. Chances are, there is not a capability for this because you want to adjust the position of the GPS receiver in reference to your car which can point in any direction.