There are a few here who think that:
Paint The possibility of a bent rim or broken spoke perhaps Or the interest in avoiding non designed pressure points
Is more important than braking effectiveness.
No problem. Select your priorities.
I don't think a fender washer will change much in the way of restraining torque. The washer should just match the contact areas.
Having ridden a few bikes where the center pull pivots ARE brazed onto the stays or fork legs, I will say this method does improve the feel of any caliper so attached in comparison to a bolt on at a single central point application. Bikes built this way and using center pull brakes are better off than the same brake bolted on, maybe in an extreme case of a bent rim they will suffer too, but when the rim is bent that much some lost paint is a minor problem.
Having the brake base "plate" contacting the seat stays takes the cantilever out of the system, closer to a brazed on pivot solution. Select your priority and go with it.
John Jorgensen
Torrance Ca USA