Lets assume 45mph multilane road, no intersections ahead, your right is bounded by a curb. You are traveling 20-25mph.
Driver behind has slowed to your speed and waiting courteously (no honkng, no tailgaiting, turn signal on)to pass. There is not another vehicle immediately behind them. Adjacent lane has moderate and continuous traffic flow.
Lane width is not wide enough to share without cooperation, but not so narrow that the passing vehicle needs to significantly move into adjacent lane. (Of course how much they do depends on how far right you move, that is why I use 'significantly' instead of defining vehicle and lane widths)
I know there are so many variables that it is really one of those 'have to be there', but I am thinking more generally - at 25mph will you put tire 18-20" from curb?
I general in this situation give myself 2-2.5' from curb, on the larger end usually. If a driver is cooperating, should I go closer?
To be clear: For a NOL there is no decision, passing vehicle needs full or substantial part of adjacent lane to pass. For a WOL (BL striped or not) there is always enough room to share even with safe clearance from curb. But what about those in-between lane widths?