Ethical considerations are important here. Using Mian Xiang for personal growth vs. making snap judgments about others. It's crucial to approach this practice with respect and not as a definitive science. Maybe Koppel emphasizes the importance of combining Mian Xiang with other practices like Feng Shui or Traditional Chinese Medicine for a holistic view.
Also, the balance between the left and right sides of the face is important. If one side is more developed, it might indicate different inclinations. The three major parts of the face could be considered for different stages of life—forehead (early life), middle face (middle age), and lower face (later years). These are common elements in Mian Xiang that I should include. Lectura Del Rostro Mian Xiang Monica Koppel.pdf
I should mention the use of the "five elements" theory (Wood, Fire, Earth, Metal, Water) in analyzing facial features. For instance, a person with a prominent Fire element might have a warm complexion and quick speech. Each element corresponds to different characteristics. Ethical considerations are important here