G2

I am trying to use G2, and I suspect that I am not the person to be perplexed. I am using a .125" end mill and I want to cut a .6" diameter depression. My first assumption was G2 i-.3 j0 f5 after dropping z .1" into the top surface. That cut a 0.709" wide depression. I can see that the end mill is starting at the center of the ring that I am cutting, but that would mean the inner diameter would be .6-.0625" and the inside of the outer ring would be .6"+.0625". Instead the inside diameter is 0.495" and the inside of the outer ring is .709". Can someone explain the path to G2 enlightenment?

Maybe this is a little help to understand direction (CW, CCW) and cuttercompensation.
forum.linuxcnc.org/20-g-code/38869-g2-or-g3?start=0#164639

G-code movements are generally defined by the center of the tool. The exception is if you add tool compensation like mentioned above. But that adds other complications such as lead in moves. It may just be simpler to include the tool diameter in your code.