Zero',
In such situations (remember, I ride on the right here in 'Merka), I'll sometimes put an arm out at about a 45° downward angle, roughly halfway between signaling a left-turn and a stop. This has the effect (I think) of making me appear wider (much like raising your arms to look taller and more intimidating to a threatening, aggressive animal!). If the car then doesn't go out a bit, at least I have a hand free to push off from the car (I've done so on more than one occasion) and at least avoid getting clipped by the sideview mirror.
The law varies by state here, but mostly, cyclists are required to ride as far to the right as "practicable" unless they need to avoid a hazard (flash-opened car doors come to mind). Things are improving a bit in some places Stateside but not in others, where bicycles are viewed as sidewalk toys intended for children or expensive sports toys intended for adults; neither of which "belong" on the road (Oxford, Mississippi and Cedarville, CA in the view of some residents who yelled at me for riding in the street
at all, anywhere). When I was planning a tour through Utah, a quick review of state traffic laws there revealed
cyclists are required to yield to all other vehicles, rather than vice versa.
There were times while riding in congested parts inner cities of The Netherlands when clearances were tight enough I was tagged by rearview mirrors as the cars literally scraped by, one time putting me into a traffic divider as the fietspad merged from off-street to on-street and back again and another by a young woman actively using her cell phone while driving (*very* unusual there in my experience at the time). I had a long-lasting bruise on my hip by the time my tours there ended.
Here, car drivers have a disconcerting habit of adjusting speed and timing so they pass when directly opposite a cyclist, making things tight for all. Also, on rural two-lane roads, oncoming cars who are passing tend to pass cars widely, sometimes dropping a wheel over the fog marker at the side of the oncoming lane. It's a heart-stopper to see a car coming at you, going 70mph/113kph+ with one wheel in the very lane you're riding, usually alongside a ditch, preventing easy escape. Yikes!
You asked...
Is it wrong to cycle close to the middle of the road in these situations to prevent motorists from actually trying to overtake?
...and then opined....
Im sort of weighing up the balance between my own safety and being a good road user.
The perfect solution, I think! Sometimes a cyclist can better weigh if it is safe to pass than a motorist can. Also, sometimes the cyclist is subject to road hazards (storm grates, broken glass, etc) a car driver cannot see. I think consideration going both ways would help a lot.
Stay safe out there!
Best,
Dan.