For thermals I use a hand warmer, actually a toe warmer because they are smaller, in the winter and in the summer I take and cut the finger out of a surgical glove and stick an ice cube in it. The glove finger holds the water as it melts and it's still visible. It's a very small 1"x2" target so once you hit it you're really getting it dialed in.

As for the question about the Photons, you need a high contrast target. A normal paper target with a grid works well but also a piece of cardboard or posterboard with a piece of electrical tape for the bullseye works too. What doesn't work is the shoot-n-see type targets that knock off orange or green when you hit the target. They are ok out to about 30-45 yards but past that you can't see anything but a black circle or square. The thin little lines don't show up. High contrast between the target background and the bullseye is key.

Jason