The structure and method which improves the film thickness uniformity or thickness control when using magnetron sputtering by adjusting the distance between the magnetron or a portion of the magnetron and the sputtering target to provide an improvement in the film thickness uniformity. Shimmed rails, contoured rails, contoured surfaces, cam plates, and cam plate control followers are utilized to achieve an improvement in film thickness uniformity or thickness control due to anomalies in magnetic field as a magnetron assembly moves back and forth when sputtering substrates (utilized primarily for rectangularly shaped substrates).