What I do is cut a 1"-2" square of tin foil stick it on a cardboard box at 50yds, if on the white hot setting it will show black, I then get a rough zero using this. Once on target, I move the target out further using a drawing pin, felt nail, screw, etc into a board with a smaller size, don't push it right in or you will heat the box/board, then heat it with a lighter just the tip (requires a friend, give it 15 seconds to cool the initial excess heat and him/her to get out the way, then fine tune your zero on it at 100yds...
Thermal targets are pretty much pointless unless you want to. w