The loss of the ridge in briar is probably due to the difference of materials. Clay is molded, briar is carved & sanded to final form. Ridges are difficult to sand. My understanding of the point in clays was to give a cool appendage to hold as clay gets very hot. Not really needed in briar, but like fins on a 50's car, they lived up to form before function - something the Shakers were very good at reversing regarding Victorian furniture.