Identify the landmarks on the skull front and back that should be covered by a helmet? posterior head? how far above the eyebrow

Protection for the head is needed in cases of direct collision sports like hockey and football. Collisions with another player or the turf may result in a concussion, thus all the helmets must possess NOCSAE certifications.  

The helmet should fit comfortably around all the segments of the player's head, there should be no gaps between the head and pads. It should cover the base of the skull, the pads positioned at the back of the neck should be comfortable, and at the same time should not be uncomfortable.  

The helmet should not come down over the eyes, the front edge of the helmet should be 3/4 inch or of two finger widths above the eyebrows.

not sure if this what   you'r looking for would be percent composition