I found that being too far away and landing the right hand with my arm extended aggravated my knuckle. Extending your jab fully- as far as you can- will generally put you in a pretty good spot. That may seem counter-intuitive but it is true. Also, turning your hand so that the proper knuckles land, regardless of the range. The double end bag is good for this, hitting it with different punches at different distances and getting your hands right.