KX100 gearing

I'm transitioning my son from a KX85 to a KX100. I noticed that the stock gearing on the 85 is 14/50 and on the 100 it's 13/51. The internal transmission is identical on the 2 bikes.

I'm confused why the 100 would effectively have a 5 tooth larger rear sprocket? I would have expected the 100 to pull a smaller rear sprocket with it's increased torque.

Think it's because Kawasaki is gearing the KX85 for MX and the KX100 for woods riding?

If you ride a KX100 on flowing MX tracks, what gearing do you recommend as a starting point?

Thanks, Mark

Ah, thank you. I didn't realize that the size of the back wheel factored in.