I'm almost embarrassed to post such a simple design … but it works for me, so may be of use to others.

The PIR Sensor on my outdoor light was detecting way beyond the boundary of my property.

This is a simple blinker to narrow the direction and field of detection to a much closer zone.

Better printed in a darker material.

I printed in white and had to colour the inside with a sharpie to get it to work.

The brim around the bottom is for double-sided tape.