M/P was always regarded as a tougher prefix. Years ago it was higher than it is now, $120 I recall. Possibly, it was a regional quirk whereby more were in the west than east, and east is where most of the pricing panel were from. They were always quite plentiful in the west, and nobody paid the cat value for them. It is also possible that a predominant market maker had a bundle when nobody else did, suggested the run was short, then leaked them out after the price went up.