Not that I don't believe you (because I've always felt side by side pairing makes sense too), but where in the paper was it indicated they would be located in pairs?
I assume it's not in the posted images, I can't see anything obvious indicating it
The first picture shows the left side of the opening aligned with the sub's centerline. The right side slopes down the side of the sub. The diagonal lighter gray shading denotes the 'edge' between the top and starboard side of the sub. The top right note also translates to 'sub side'.