I think what exo is trying to say is that the system hair doesn't always "flow" like natural growing hair. Unfortunately no matter what you do the hair won't always behave the same way that yuor natural growing hair does.

This was much more of an issue for me when I wore a partial unit, but even wearing a full cap I always use styling product. When you add product to the hair on the unit and to your own growing hair it controls the hair movement making the two appear more similar. With my full caps it allows me to position all of the hair the way I want it for maximum realism.

I know a lot of people are hesitant to use hair product because they don't want their hair to look crunchy or greasy, but if you find a product that gives the kind of hold you are looking for and use it sparingly you would be surprised at how natural it can look.