I cut mine at not quite 45 degrees. I started with the bottom horizontal strip, then the two vertical strips,finally the upper horizontal strip. By not cutting at the full 45 degrees, the lower ends two vertical strips slightly overlap the ends of the lower horizontal strip. The ends of the upper horizontal strip slightly overlap the upper ends of the vertical strips. This leaves a "shingle" situation.
When I put new glazing strips around the windows, I was replacing three of the five windows as one was broken, and two were plastic. One other window was removed easily as the adhesive was sun-baked, so that new adhesive could be used on all but one window.
None of my windows leak.