The one area I can comment on is having a small amount of real frontal hair with my hairpiece.
I use to shave it all and it looked ok but not quite as realistic. Then I figured, hey with the little bit
of real hair I have I should be proud and show it off. So I let it grow back and now place my system just behind about 1/2 inch or so. You have to place it accurately or you will have a space between the two areas. I have that alot but not really to bad to deal with. There are advantages and disadvantages.
The advantage is the hairline is flawless because it is my real hair. It hides a goofed up frontal area hairline as it frays or gets a bit messed up.
The disadvantage is that no matter what it does not blow or move 100% like the system hair( although I now have a Toplace unit that helps alot in this area). Exercise is another issue. The real hair can get wet and may show some seperation from the system. It may fall on the forehead where the system hair is still looking good. I usually just swipe the sweat through the hair to help blend.
I say try it behind at first, then you can always shave it off later.
Hope this helps