Thank you Marianne for the information.
About flexi prims: When looking at my old flexi hairs I have noticed that many of them have very high ARC. However there are some hairs where the ARC is very reasonable. The ARC seems to depend on how much the prims have been tortured. Curly hairs are the worst, straight hairs have a lot lower ARC. I love the hair what I have in my profile picture, straight one. Most of the hair prims go to back of the head and thus the disturbing "cuts through the body issue" is almost non existent. And I love its movement when dancing, it looks quite natural. Pretty cool one.