The top left shows Tims sketch put in place as the hip was intended to be seated. The design requires it to be seated flush or it becomes to wide and causes a complete redesign of the thigh thickness or the pelvis width.

Below left shows how you would have to attach Tim's sketch to get it to move. The attachment point would have to be greatly reduced making a weak joint for the model. And all for a few degrees of movement.

To have sufficient contact the ball would have to sink in half way thru the pelvis and the ball would have to stick out sufficiently to allow for clearance along its face. It can be done, but again at the cost of changing the look of the piec greatly and redesign of the model, all for the movement of one piece that ends up being glued.

If the customer wants hip movement, they can probably model it by scratch and have it end up looking better than the joint would look to allow it to move in any position.