the lighting is fairly near zenith so its reasonable the entirety of the shadow would be cast on the hull. the curvature of the hull itself would diffuse the shadow quite quickly as well.
hi sutton is an accomplished artist with a good eye for proportion and solid understanding of visual fundamentals. i would not dismiss his visual analysis out of hand.
But he still insists that the diameter is 10-11m. There is a full-size J-15 model near submarine as reference.