This is not how it works. As explained in this post by UnstableVoltage: Shots too random.
“The spread within the cone works on a bell-curve with highly inaccurate shots being as unlike as highly accurate shots (meaning that most rounds will tend to fall somewhere close to halfway between the red circle and the bullseye).”
In other words the centre of the yellow circle is the edge of the bell curve since it’s just as unlikely as the outermost point of the red circle, since these are the “highly accurate” and “highly inaccurate” shots he’s talking about.
So, really it is 50% for each circle but it’ll be a tight spread around the ring of the yellow circle with very few shots landing in the centre of the yellow circle or on the extremities of the red circle.