Bryce, What you say does sound logical from a pure mathematics standpoint. However, there is more at play here than just the rim diameter. There is also the height of the sidewall.
If precision is required. LOL......then I will quote the Op Manual which states "Minimum Ground Clearance at Gear Case...7 1/8 " for 220, 222, 224 and 11" for 444.
That is a 3 7/8" difference
In order to level the tractor out, a different front axle and spindles were used which increased the ground clearance at that end. The trans-axle housing is the item that hangs the lowest which is why the ground clearance is measured at that spot.
Thanks for posting.