On the narrow mountain roads in the SF Bay area where I ride a lot, I ride as you describe (in the right tire track) when climbing slow. I have a helmet mounted mirror, which I use religiously, although I can hear cars coming. If a car comes I wait till the last moment, then move to the side. I try to leave lots of room in case there is another cyclist decending, I don't want to force the car to head on the opposing cyclist. If I am decending fast, I take the lane, usually I am faster than the cars.