Tooth pattern should fall right in the middle on both sides. The back side of the gear teeth is the coast side, which loads during deceleration. By the way, there's no guarantee a ring and pinion set will break in properly, although most do just fine. However, if you don't work-harden the gears properly during break in, you risk gear failure. Work hardening means hard acceleration and deceleration once you have 500 miles on a rear end.