The closest civilian equivalent I know are military rifle matches at held at Camp Perry and around the country by the CMP. The positions used are the military positions. The hardest one is standing, commonly referred to as offhand. Prone and sitting are easy, you can use the ground or your skeletal frame to stabilize the rifle. Offhand, the barrel of the rifle is out there in the air and you are standing. It creates a wobble in the barrel that must be dealt with to get good hits.
The Army, Marine Corps, and the CMP all teach an odd posture. Leaning back, you set your forward elbow on the point of your hip bone, then tuck the other elbow against the rib cage. To then get a sight picture, the butt of the rifle rides up on the shoulder. In sport shooting, you wear a stiff jacket to further stabilize your torso. This minimizes the movement of the front sight.
Once in the position, rather than try to stop the front sight movement, you control it, creating a small deliberate movement so that your trigger pull ( yes pull) occurs when the sight picture appears correct. It is hard to do and very hard to do well.
Here's the picture of my son in that position, followed by several pictures of the USMC Shooting Team, the Army Marksmanship Team, and some civilians shooting military rifle matches I found in a Google search.
It's unfamiliar to a lot of shooters and even though I only saw one comment on the topic, I know some others were thinking it, so I offer this information to explain his position in the photo.