Mission 3 Spy Academy: Practice range targets

Does anyone know how to get this medal? I've found five targets on the southeastern islands (two each on the closer islands, and one on the farther). I've tried shooting them all from multiple locations, including the very top of the cathedral above the final mission objective, and from the sniper tower that all targets seem to be facing, but still no medal.

Are these not the targets that you need for the medal? Do you need to hit them from a specific location? Am I missing any? Does anyone know?

Here's how I got it

https://www.youtube.com/watch?v=hQva9bITqGY

There are 5 of them but it didn't work for me in a current save.
Restarting the mission and shooting them again seemed to work for me.