Most better quality sidepulls should be easier to keep centered because they usually have much better pivot designs that have smoother action. and will return to center better than cheaper made sidepulls with crude pivot bearing designs. I never owned Superbe sidepulls, but I would be surprised if I cannot keep it centered on a bike. All my sidepulls since the 80's were no problem when it comes to keeping them centered. Also check your brake cable routing and make sure that the sterring action on the front end does ot pull on thern too much which could also pull your calipers off center.

Chombi