Yes, on the ground. The purpose of this is to learn how to instinctively shoot a small object at an unkown distance. You can think about it this way, How do you aim when you throw a rock? Answer, you don't. Your mind automatically tells your arm how hard to throw it in order to hit the target. By shooting at a tennis ball or stump shooting, you are training your minds eye and your muscles to automatically push your bow arm to the target in order to hit it.

The fun part of traditional archery is being able to cant the bow as much as you want and still hit the target. We lay on a stomachs with the bow parallel to the ground, bend backwards, shoot opposite hand. Anything to improve your shooting and mix it up for fun.