The two sizes of the Cross Top levers are listed by the size of clamping portion of the handlebar, this does not reflect the actual size of the clamp on the brake lever.  All road (drop) bars taper from the canter portion of the bar to a smaller diameter, this narrower section of the bar is the intended position for the lever.  Therefore the lever can be purchased based on the clamp size of your bars and should fit the bar on the narrower section.