My thoughts on it, don't think it's right but... It's like xl monty pads and the short ones, they both work equally well (probably) because what the long lacks in concentration of pressure, they grab it back with more surface area and vice versa. Same with disc, small surface area = large pressure on one bit, and vice versa. I think that's a fairly good explanation of it, nice and concise, but i think i remember a respectable forum member, think it was either Tomm, or Janson rings a bell, telling me i was wrong. If that was infact a shit explanation, do tell and i'll try write a better one.