I'm not sure that OD defends JR. Frankly, I don't think JR is defended by anything at all. JR is a measure of how easily or not a player can score outside the paint.
Speaking from memory at this point, but the statistical analysis on three point shots on the USA offsite did show OD as the relevant defensive skill against 3 point shots; an uncontested three point shot was mostly influenced by jump shot rather than JR, while a contested three point shot was mostly influenced by JR vs. OD. This is why a low JS/decent JR big man can often shoot a very high percentage from three against a very low OD big man.