Yoga by Brenna

If the engagements of the posture are correct, you are doing it right. If the relaxations of the posture are correct, you are doing it right.

Depth is not something to strive for on its own. It is not only necessarily a sign you are doing it right. Depth is only the result of correct engagements and relaxations.

Practice the postures to learn how your body works. Correct engagement and relaxation is the goal.

USHTRASANA
Dr. Gouri Shankar Mukerji (1927-1998)

Dr. Gouri Shankar Mukerji instructs:
Kneel on both knees, keeping the upper body completely vertical to the ground and the lower legs touching the ground up to the toes. The distance between the knees should not be more than 20 centimeters (8 inches). Bend the upper body back until you reach the heels with your hands. The thumbs should be inwards while the fingers must be outside on the soles of the feet. The thighs should remain perpendicular to the ground.