Put it wherever it feels best.
I place mine on the back of my phone, tablet and computer screen. Even after a long conversation, my iPhone does not get warm and I don’t have that yucky feeling that I used to get after using my phone.
Philip and I have been transferring our shields from one iPhone to the next over the years and they keep working! Adding new adhesive is advisable. We use Scotch Extreme Mounting Strips, Double-Sided Tape for a durable hold.

