"The bird is to taper gracefully and be well proportioned according to the pictorial of the time, standing well off the perch , at an angle of approximately 30 degrees from vertical, with the beak tucked deep into the mask, backline sweeping gently, in a slight concave from the backscull to the tip of the tail. Bodyline to curve out from the beak through the mask to the chest and then taper back to the lower tail converts of the tail." from THE STANDARD
Posture is called the stance. Perfect posture is to line the eye of the bird in a vertical line with the perch.