As the base of my extended bosses is a larger diameter then the OEM base size I think the flex in the bas will be less then the OEM speced bases. So the portion of the canti boss that the arm slides onto being the same in both cases will have the same flex, in both cases. No additional flex with the extended base bosses. (and actually my feel suggests that my extended base bosses actually flex less then the OEM ones do). But adding a booster arch is always a good idea and can often reduce the squeal that some brakes have. I have wondered why booster plates haven't been more common sometimes. Andy.