MT street radial sizing help?

Can't answer the question on section width from a 9.5 to a 10 rim. It can't be much as it's .25 on each side.

I think i've seen something from M/T that said rims need to be within 1" high/low of tread width. My friends are running 275's on a 10" wheel with no problems. Only goes 10.60 with a small black.