MOA is a unit of measurement to describe the angle of the cone which projects the circle onto the target. That circle can be measured in inches, but not actually measured in MOA. Defining MOA dispersion REQUIRES a relative distance, else it cannot be defined. Equally, inches of group size, whether diameter or radius, are largely meaningless without a relative distance - a 1/2” group might seem great, but if it is fired with a $5,000 rifle at 25 yards, it’s crap. A 10” group might seem poor, but if it was fired at 1400 yards, it’s great. Frankly, radius of the group does matter. First, we cannot have radius without diameter, and cannot have diameter without radius. Radius reflects the dispersion of the shots from their centroid - and we typically try to place the centroid of our group onto the center of our target - aligning POI to POA. In MOST applications, we need to understand how far from our POA that bullet will strike. In hunting, I don’t care about diameter at all - I want to know that if I aim at the center of where I believe the heart to be, my bullet will still land within the edge of the projection of the heart. In PRS competition, I need to know that if I aim on target, my bullet will land within the edge of the target. In Service Rifle competition or Benchrest or F-class, I need to know my shot will land within the edge of the scoring ring. In EVERY case, the radius from where I will center my “cone of dispersion” on the target - where I place my POA - to ensure the RADIUS of the cone does not slip off of the edge of my target, whether that’s a heart, a steel plate, or a scoring ring. Only in Internet discussion of group size does group diameter really come into play. Not entirely apt, despite the lies we tell ourselves as shooters. The firing system always involves something which supports it and fires it. When I shoot a rifle, the resulting groups on target will be more precise than when my 8 year old son shoots it. When I shoot my rifle, standing while supported on a barricade, the resulting groups will be less precise than when I fire prone from a bipod and bag. Even when I shoot prone from the bipod and bag and I’m dropping shots into one hole, I’m part of the equation - as my son won’t deliver groups as precise as I, even prone. On days when I have not slept well or don’t feel my best, my groups open up. Even locking the rifle into a vise and firing remotely, the resulting remains dependent upon the stability of the mechanism firing it. So we tell ourselves that Precision is only about the rifle and load - because in theory, the rifle will disperse shots within the same statistical deviation regardless of the shooter, but it really isn’t. We can’t actually measure that raw potential Precision, so it becomes irrelevant. Equally, we know we can influence velocity and POI simply in how we support and fire the rifle - so it’s not fully true to claim even the raw precision of a rifle and load is completely independent of the shooter behind it.