Ok, I am looking at the Sacrum of the spine which is behind the pelvis. So, there is nothing closer to the surface of the pelvis/spine area Although, The surface of the back must be a more accurate way to look at the spine , especially the sacrum than the Face On View. You seem to not agree with this.
Since the spine is not a straight line, the bottom part Sacrum can move forward as lumbar moves back. (like turning an 'S". Yet this may not be completely accurate since you can stabilize the spine and have rotation within the spine itself.
If the Sacrum moves forward in the backswing, and the belly button moves away from the target, this would mean that the lower spine moves forward, and the mid spine lumbar moves backward and possibly internal rotation in the thoracic area from mid backswing to top of backswing. (not much though). (I only say this due to the fact that the hips stop turning at some point in the backswing but the backswing continues).
What is important is the fact that the Sacrum moves forward and then backward to impact due to rotation. This has been my point all along. Most students don't understand this and try to slide the Sacrum when people say "lateral".