ran Petersen SE on my touring cargo bike , what made them work better
was thicker tube walls where they, their bosses are mounted on.

Happened to be a flying saucer like Boss with a flange all the way around
in the builders parts bin, to mount the brake against when they were fitted. ..

the SE uses a helical driver around the frame boss, there is no spring anchor pin..

the fitting used star washers ,I got to dig into the surround ing boss flange.