I would love to have this standing statue of Ma'at for my altar here at home... It's generally understood, when you find a statue of a god or goddess holding a "form", they are aligning themselves with the cosmos. In regard to images that you find standing, such as this one, the god or goddess (or Buddha) is more or less establishing a final order. With standing Buddha's for example, the view is that the standing position means it is the Buddha's choice to make it his or her last lifetime. The standing position represents the final judgment, and the ability to come into the light.
The kneeling position of Ma'at is very similar, if not the same, to many statues of Isis. This "form" is showing Ma'at going into a contemplative position of giving birth or new life to a situation. The sitting position represents the ability to go inward, to look into a glass darkly and come out the other side, where everything is eventually revealed to the light.