There was a study done some years ago by a couple of LAB instructors where they made hundreds of passes through the same stretch of road, starting at the gutter, and moving farther left by 1 foot increments in successive passes. What they found is that when you move just a few feet out from the gutter, motorists still think they can squeeze by and they end up passing you with less clearance. But when you get even farther out, towards the center of the lane, suddenly motorists tend to change lanes to pass because it's clear from much farther back that a lane change is required to safely pass.

I generally ride near the left edge of the green zone shown on the right side of this diagram (a bit farther left than the cyclist shown), 2 1/2 years later and it has worked wonderfully for me: