Sometimes the engineers at the Mothership think in mysterious if not downright inscrutable ways. This fisheye exemplifies this with regard to the mounting arrangement, as clearly demonstrated by Erik. A similar case exists for the first versions of the mighty 360-1200 mm f/11 Zoom-Nikkor. The lens is very heavy and the slanted tripod foot is for once very sturdy. However, this apparent clever design is marred by the tripod foot that only has a single 1/4" screw hole and not a very deep one either, plus the base platform for mounting is set off from the major part of the foot so as to make a minimal contact area. What kind of engineering thought can explain such a silly arrangement? I had to redo the foot and the mounting arrangement completely.
Pleased to learn you have done the Nikon engineers one better so we can enjoy the 6/2.8 to its fullest extent in the near future. Really looking forward to what the lens can do for "ordinary" as well as not-so-ordinary photography.