This has nothing to do with fiber type. Many people have reported it so far. It's just the nature of the lift... more muscles are involved in the high pull so you can compensate more easily. Furthermore there is a different between a 100% on a high pull and a 100% on bench since on the high pull you must be able to accelerate the bar, so a 100% on a high pull is probably more like an 85-90% on a regular strength lift.
Finally on high pull it is a little bit less clear what constitutes a good rep. Sometimes you wont even notice a 1" difference in pulling height, but that 1" makes a huge difference in the amount of force you need to produce. On the bench it's pretty clear whether you get it or not.