Largest Ring Option In Flare Tool

In the Adobe Help Guide, it is stated that the "largest ring" is calculated as a percentage of the average ring. However, when experimenting, I noticed discrepancies in the results. For example, when creating a flare with a 100pt diameter, 5 rings, and setting the largest ring to 100%, with the path set to 300pt, the calculated ring sizes are: 10pt, 10pt, 75pt, 150pt, and 300pt. When I calculate the average of these rings, it comes out to 109pt, but the largest ring is not 100% of this average size. Could you clarify how Illustrator calculates the largest ring and why the results seem to differ from the described method?