Scary indeed!

On a busy stretch of road where I often ride, at the top of a hill AND in a curve, I was passed recently by a double gravel truck. That's a gravel truck with a trailer in the back which is as big as a second gravel truck. Drivers there are used to sharing the road but this guy just wasn't really careful.

In general, the further you are from the curbside, the further the cars will be from you on the other side. Bonus: if they do try to shave the fuzz off your forearms as they pass, you have somewhere to go on your right side instead of being stuck on the curb. A good 1 meter - 3 feet is what I think is best. No matter where the line is (if there is one), I ride about 3 feet away from the limit of the paved road to the right.

This being said, there will always be gonzos that don't remember that bikes were invented before cars. Keep your line and hope you'll be fine!