I do not think the head size has anything to do with the girls with PCS issue. I think it has more to do with fluctuating hormones. The balance between progesterone, estrogen, testosterone, etc changes throughout the month for women. These same hormones effect how the brain functions. If the balance get too far out, symptoms would be greater.

As far as the high achiever with PCS issue goes, my neurologist said that my brain is very high powered frontally. My concussions have left it underpowered in the rear/occipital lobes. This leaves a serious timing differential between the two lobes that disrupts the proper functions. I also have a damaged 'gating' system that blocks or allows information to flow to the frontal lobe.

The occipital lobes can easily get overwhelmed with information. This prevents any of the information from being processed, sort of like a bottle neck.

The high achiever also has habits of depending on the high function levels. If these expectations are maintained, the errors are blatant. If the high achiever is able to lower their expectations a bit and moderate the environment, some of the frustration can be reduced.