First: Good work!
But there are a couple of extra variables that are clouding the picture. Besides the tire size difference, there is also the difference in brand and tire type.
Were the Dunlop's the OE tire? That's another issue as OE tires are typically better for RR.
Bottomline: Be careful about characterizing this test as about larger diameter tires. There are other things that might be affecting the results.
Nevertheless, thanks for doing the work and sharing.
Since I had done some work on tire size vs RR, I was wondering if I could quantify what affect the tire size alone had on RR.
Here's where I got the formula:
Doing the math, the change in RR due to tire size is 5.4%. So maybe the affect the difference in diameter is much smaller than you think.