Definitive reference for tire widths?
I have had similar issues with mountain bike tires. While the industry seems to have done a good job of standardizing rim sizes, tire width seems to vary. One brands 2.0 inch tire can be larger than another brands 2.1. Of course there is some variances with rim widths and tire pressure and tread design, but overall it seems there are no meaningful standards for width. This is where a good relationship with your local shop can be helpful. They may allow you to try sizes and brands to find a good fit. The added cost of buying locally may be offset by not paying return shipping.