...Sony FE 16-35mm F/4 zoom, while the lens is about as big as a 16-35 for DSLR housings it can be used with a much smaller 180mm port with results as acceptable as the 16-35 on DSLR with a 230mm port. This is a result of the shorter distance between lens and sensor in mirrorless cameras like A7R II.
"This is a result of the shorter distance between lens and sensor"
Can you explain why this is so? I remain skeptical.
The lens has a very large diameter and thus may require a special port and port extension tubes for your housing adding more to the cost than just the lens. This may be one reason why we have not seen much published. It may be more useful for those shooting video when the video mode does not use the full size of the sensor. The 8-15 is much easier to adapt and works well under water.