Hi Throwaway, here is my attachment technique, which you may find helps.
Basically I put the tape on the back and sides of the hairpiece. Then I place the hairpiece in perfect position and anchor it with 2 small pieces of tape. Then I pull the backing paper off the rest of the tape and stick the back and sides. Then I glue the front. Here is the method in more detail:
First, I put the tape on the back and sides of the hairpiece, leaving the backing paper on, but I fold over a corner of the backing paper on each bit of tape.
I also put 2 small pieces of tape (about 1 square centimetre), one on each side of the piece, about the middle of the sides and 2 centimetres from the edge. I take the backing paper off those 2 small piece, and give them a spray of alcohol.
I then put the hairpiece on my head and move it into perfect position - no gaps or overlaps. The alcohol stops the adhesive on the 2 small pieces of tape from sticking immediately, and gives me a few seconds to move the piece around. When I get the perfect position, I press down on the two small pieces of tape and stick them into place. They then anchor the whole hairpiece.
I then flip up the back, pull off the backing paper on the tape, and stick it down - sides first, and then the back.
I hold down the front of the hairpiece with one hand, and mark the position of the hairline by digging marks into my forehead with the thumbnail of the other hand.
I then flip the front up and clip it out of the way.
I apply a layer of glue using the thumbnail marks as a guide; dry it with a hairdryer, and repeat. Then I spritz the glued area with alcohol, and bring down the hairpiece hairline and apply it onto the glue - middle of the hairline first, and then the sides. Then I press the hairline firmly into the glue with the teeth of a comb held sideways.