Here is a more detailed description of my method:
Go to You Tube and type in "invisible part method". There you will find a few videos describing this method. However, instead of placing the hair directly onto your own hair, I place mine on wefting tape first and then apply the tape to my crown area.
I initially started with a 3/4 inch tape, cut it in half, and then applied wefts to the tape. Unfortunately, I found that there wasn't enough hair to give me the fullness I wanted in the crown. So, next time, I used the 3/4 inch tape and cut the wefts to fit. Now, I also found that if you place the wefts at a slight angle as opposed to straight up and down, you will get more "lift" and "fullness".
You can either place the wefts touching each other, which will give you so much hair that you will not know what to do with, or you can leave a small space between the wefts, which is what I did and I will tell you why below. Now, I really use the extensions for a little fullness, not length. So all I use now is one row of these wefts in the crown area. Even with just one row, my hair is so full!!! You will see what I mean when you do this method!
Finally, the reason I place a small space between the wefts (and I mean small), is (1) placing the wefts back to back gives you so much hair (and I didn't need that much just for fullness); and (2) when you start wrapping the tape around to the back of the head, you can cut small slits in between the wefts (at the bottom of the tape) to keep the tape from bunching up at the top. You will have a smoother application this way. However, I have found that the wefting tape is stronger and slightly thicker and does a superior job for this method.
I hope that I have given you a clearer picture, without a picture (LOL!!!) of how I do this method.
Good luck and let me know if you have any other questions.