Thanks - after squinting at it some more and flipping the wheel back and forth to make sure it isn't a dish issue, I think you might be right - something about the fork is slightly asymmetrical. Noticed also that the angle of the spring receptacles on the posts are not aligned (one is rotated several degrees around the post from the other).
I guess that's what you get on a no-name carbon fork on a mail-order bike
I can adjust the spring tension so that the yoke is centered, but then one brake pad is touching the rim when the brake isn't even applied. Again, not a dish or axle-in-dropout issue.
I've removed one thin washer on the brake pad threaded post on one side, and will see if that does the trick.