I remember seeing something a while back about the 150 and off axis audio. You didn't mention what you are using for fronts and whether you have calibrated the speakers using an SPL meter (if not, you should do this).
Also, try moving the 150 a little in front of or a little behind the fronts (in relation to a straight line across all three speakers). If the 150 is in a fixed position, move the fronts forward or back. The purpose is to allow the 2 fronts to help fill in the soundstage on the sides. This exercise works if you calibrated and you will need to recalibrate when you find a sweet spot.
