Thanks for the vote of confidence, Baby Diesel,
First, here's my webpage on the subject of tire size and RR:
Barry's Tire Tech
Short version: Compared to other things - like the composition of the tread rubber - SIZE is a pretty small contributor in RR. single digit percentages vs double digit.
I developed an equation based on some data - and based on that, sidewall height is counter proportional to RRC. That is, taller tires have less RRC.
I generally refer to all of this as "Bigger Is Better". So if you want to minimize RRC, choose the biggest tire that will fit under the fenders - BUT - careful selection is much more important. Spend most of your time there.