For your 6 Iron, you should use a level setup with a 50/50 weight distribution.
As you move closer to the green, you will start using your shorter clubs. To ensure solid contact, shift your weight slightly to the left. This will give you more of a descending blow at impact.
With the 9 Iron, you will want a weight shift distribution of 65/35 with your body leaning more to the left. This brings the club into the back of the ball for solid contact.