Your 90/90-19 = 25.5" is closer in diameter to the stock rear 110/80-18 =25.2" and sure looks great. The OEM front 90/90-18 =24.4" does seem a bit puny for a Bullet.
The Indian Classic 500 (US C5) does seem to look a bit more robust with a 120/80-18 =25.7" rear as OEM.
And that rear tire their using WOULD have a larger contact patch
I wonder if they went to a wider rear Rim ? You could probably put a 120 on ours with out a problem.
I have looked at mine and there looked like plenty of room. Do you know what brand tire they are using?
Yeah it looks like a 120 would fit on the rear rim.
http://www.dropbears.com/u/utilities/tyrerim.htm