A mold includes a forming insert that includes an upper portion and a lower portion. The upper portion includes a sidewall segment and a heel segment extending from a bottom of the sidewall segment. The sidewall segment has a sidewall radius, and the heel segment has a heel radius that is less than the sidewall radius. The lower portion extends axially downward from the upper portion to define a base cavity. A forming base is positionable within the base cavity. The rim has a rim radius that is less than the heel radius and the step has a step radius that is less than the rim radius.