[vj]

The degree to which the upper spine is bent from horizontal will create a plane angle. Meaning, if my thorasic vertebrate (upper shoulders) set 14 degrees from horizontal my plane angle will be 76 degrees or 14 degrees from vertical.

From here if the shoulders move around the spine (which a broad definition of what is happening) the sweet spot of the putter will travel back-up-in, on the 76 degree plane angle without the sweet spot being moved from plane. The same will happen on the way through.
Hence my belief in the left shoulder plane angle from Mr. Kelley.

But remember, 7-13. The shoulders should be monitored.