they reduced the small diameter on the cam lobe so that the highest lift point on the lobe will not be larger from the camshaft centerline than the bearing journals. If you were to take the high lift cam and roll it on the table, they didn't want the lobes to make contact with the table. If you kept the stock base circle and kept grinding taller lift lobes, it would get increasingly difficult to install the cams plus you you be pushing the lifter higher and higher out if it's bore. By reducing the base circle it gave them more room to increase lift.