Supine-on the ground shooting position
A third compromised shooting position is supine, basically shooting from the ground. This is best done on mats in the dojo and requires a bit of energy to get down and get up, big to train on martial art mats. There are various ways to get on the ground and off the ground as described by Gary Drake in this video.
The above noted drills can be combined into an integrated drill as shown below in the video.
Video of Sample Class Related to This Block
The sample videos below are to help you see how this instruction is actually taught. Now, this is not the only way to instruct, but it is shown to give you an example.