2.2" taller is quite a lot of inches in circumference. 8" to be exact. Static radius is what is important for gearing calculation though. The radius as measured from the center of the axle to the ground, specifically, due to squat. I'm wondering if you couldn't lower the air pressure to get the...
I would be more inclined to try a single subsoiler type ripper to go around the tree before hooking the stump and pulling on it. It puts a lot of forces into your box blade at weird angles when you have small isolated contact areas you're pulling from.
Something like this is what I have in mind.