I apologize, I read your reply wrong. I do agree with what you said. Gene.
Accepted but not needed, it's just a discussion. I critiqued your terminology and that's on me, it's a habit; sometimes it's needed but sometimes it isn't; in this case, it probably wasn't needed.
According to the formula, using the tire sizes you mentioned, a 15" OD tire with a 9:1 ratio would equate to a 10" OD tire with a 6:1 ratio; a 50% higher ratio for a 50% increase in tire OD.
15/10=1.5 1.5x6=9 Reversed: 10/15=0.6666666666666667 0.6666666666666667x9=6