Proper tan tien means proper hip and lower spine alignment. This affects the entire posture. 3D dynamic movement, so not just 2D. This part is critical, because it is a 3D dynamic and in several free motions.
After tan tien, the abdomen needs to be strengthened.
Subsequently, it is the concept that I call “free floating chest”. This is freer intracoastal (sp) muscles–expanding chest outward, and uplifting upper chest, and the entire chest being uplifted higher.
So, the entire chest is expanded. Hence, this is also the basis for the Eastern meditation methods’ focus on breathing methods.