Here's me having installed the adhesive. On the DIY Tesa Method (first photo), the fit wasn't quite perfect, but Tesa Tape is quite flexible, and so can be curved slightly once the backing is removed so that it fits in the channel. Tweezers are quite helpful for this however!

The 2nd photo is the results of the Apple Watch Adhesive Method, which I'm really happy with overall - this is with the adhesive applied (3 layers), and the backing on both sides removed. You can see it just fits the PTS, but you do have to be accurate with the placement.