Beautiful picture and beautiful posture this. My teacher often used to say that the student's bum only properly comes in with postures such as Golden Rooster when one knee is strongly raised, pulling the coccyx under, stretching and straightening the lumbar region of the back. Try doing a Form raising the stepping leg exaggeratedly (pull the stepping foot up to the knee of the supporting leg, or the groin, or touch the knee to the elbow of your ward-off arm with each step, depending on your flexibility and sense of humour).