I ride many of the same roads either solo or with my wife with each of us on our own bike or on a tandem. It is pretty clear that while lane position is an extremely important factor in the quality of the passing movements by motorists, my speed may be even more important. When I/we are humming along at 25 mph on a road with 30 mph cars, the few motorists that pass completely leave the lane to do so. When we are traveling at my wife's speed, about 12-15 mph, we are buzzed mercilessly.