Aw yes, the good ole Bay Area motorist syndrome. I too have a MS light and get my share of close call. It was even worst before the MS. It was common on both side of the Bay. Most likely you maybe experiencing the old Cellphone motorist attention disorder.

A P7 on your helmet with a quick glance at car from the side will help a lot. It really get their attention which I stop them in their track avoiding them hitting me. Along with that I also got two mini white blinkies each one pointing directing toward the side mounted on my helmet.

I also mounted two more red mini blinkies on my chain stay pointing 45 degree toward the back and toward the ground. Not only do they provide a total of three red light source (including the post light), but the reflection on them from the ground gives me two more. Since they also blinks at different rate, it is hard not to notice me on the road at night. View from the back shows five red dots and view from the side yield three red dots and one white dots.

These mini blinkies can be bought at most bike shop or Amazon which show it having clip mount but it came with velcro that can be mounted anywhere. Yes, it is a hassle to turn them on/off, but I only use them in heavy traffic area which is where I notice I am more invisible.
http://www.amazon.com/SIGMA-MICRO-W-...f=pd_sbs_sg_29
Here a view of rear (bike rear not mine lol)...sorry but one blinkies was tilted but you get the idea.