There are hazards to riding too far over to the right.
1) Motorists tend to look at the center of the lane for traffic. If you are way over, people pulling out from the driveways and turning may be less likely to notice you.
2) If you ride a bit out in the lane (about 18" from the side of the road), you have some room to manuever if there is a road hazard like a pothole or a road kill. Otherwise, if you approach a hazard on the side of the road and you have several options a) run off the road (not good), b) ride through the hazard and hope (not good) or c) swerve into the traffic and hope the motorists are on their toes (not good).
3) The other thing is something you have noticed. I have noticed this also. When I am riding far to the right and if a motorist can squeeze by me without moving over into the oncoming lane (even a little) he will always seem to choose squeezing by me rather than giving me a reasonable amount of room even if nothing is coming.
I will often move farther into the center of the lane than is my custom in special circumstances. One is if someone is pulling out from a driveway or parking lot. If I am in the center of the lane, they are more likely to see me and if they pull out, I have more room to manuever. I also move farther to the left at intersections. I do this to try to avoid primarily "right hooks". A right hook is when a motorist passes you and turns right either right in front of you or right into you.