Sitting Chi Kung gives us an opportunity to concentrate on our breathing. Oftentimes standing Chi Kung does not allow us to access our breath as consistently as sitting. We become easily distracted with discomfort or correcting ourselves or any of the myriad of distractions that arrive as in any other form of meditation.
If we can bring the depth of awareness which can be more accessible to us while sitting into our standing, we have achieved some progress.
Also sitting can give us a clearer feeling of raising the spirit ie the feeling of the head on a thread from above.
Physically, sitting can help strengthen our lower back muscles.
Sit on the sitting bones close to the edge of the chair.
Breathe into the chair.