I have two diiferent roads with faster same direction traffic.
One is narrow, so passing traffic must move into the opposing traffic lane to pass me. I ride about 18" from the edge, but if it looks like a car will be passing me at the same time as a car approaching from the front I pull out into the middle of the lane so he will slow down an d wait for the other car to pass before he passes me.
The other road is wide enough for cars to pass me without pulling out into the opposing traffic lane. If there is no traffic coming behind me I ride about 3 ft from the edge so I avoid the storm drains, which although reasonably level with the pavement are not comfortable to ride over. As cars approach from behind I move towards the edge, so they can pass easily, even though this means I have to take some weight off the saddle as I pass over the storm drains.