This has been the understood law in Missouri forever. You can protect yourself, you can confront the thief with deadly force displayed, but if you are not attacked for the thief to get to your belongings (the car) or yourself and your weapon, you can’t chase him down and maim or kill him in retribution for the attempted theft. I think the same holds in Texas if the thief is trying to flee a house.
Bullets in the back always appear as bad form.
Correct.
If they are fleeing, don’t shoot.
Now, if they are fleeing with your kidnapped child in their arms or your car, that’s a different story.