I did notice no Seventh Tire in those patterns. Found both Four and Five Tire rotation for FWD and RWD cars/trucks but not that seventh for duallys. I'd say match sizes (essentially diameters) and try to equalize irregular wear (that I figure will be on front).
Given road has a slight crown, any slightly smaller rears should be on the inside. Right rear outer probably takes the most beating from hitting things. BUT right rear INNER takes the worst beating overall. It's by the hot exhaust in many cases, but it also shoulders full load on the right rear when we run the outer wheel off the pavement.
Worst tire to Spare?