You have to think of this like a driver, drivers know that if they are turning right, they need to scan the sidewalk to the right, but all vehicle traffic is coming from the left. So, they look left, scan the sidewalk to the right, then look left again. If your going against traffic, then drivers will not see you, because they are not looking for you. This is why in places where there are contra-flow bike lanes, there will be big caution signs warning drivers to expect cyclists coming from the "wrong" direction.

If your concerned about getting hit from behind, I recommend three small investments. First is a bicycle mirror, there are two general styles, one is the glasses/helmet mount, the other is the bar mount. If you have more then one bicycle, then the helmet mount will allow you to use one mirror for several different bikes. Second is a decent rear light that has a flashing mode. Drivers have it ingrained from the start to watch for flashing lights. I noticed after running the rear light in flashing mode, and I have a cheap crappy one, during the day, that drivers tend to give better clearance.
Third is one of those day-glo orange/lime coloured construction vests. They are made of a plastic mesh so they breathe well, and drivers are also expected to look for them. They usually have retro-reflective stripes on them, and as soon as headlights hit it, those stripes light up.

Total investment for all three, is about $50. That's pretty cheap insurance in my books.