J3 is harder to hit with obviously because of the smaller hitbox. I would start combos with is because of the ridiculous cros up potential of the j2 . I mean the j2 has a very long hit box so much so tht I believe the animation will change if you cross a person over and you are so close to him his fist will hit u. Definatly one of the best cross ups in the game. As for set ups into j3 the only one I use is my bread and butter combo its good damage. J2, f22, HM, MB, b3, J3, f223, HM-42% 1bar. The j3 is where the damage comes in.