The HVX needs about a +4 to properly frame 16:9, and nothing in 4:3 modes. So the "standard" achromat will give the HVX plenty of extra room for zoom-in if required. The MPIC technically requires a macro on the HVX, but Steev Dinkins is zooming the footage in post to accomodate.
That's a good link Andy. Originally I had planned to make the rear ring adjustable for depth, but later came to the conclusion that very few cams would benefit from this feature. The spacer rings are the best solution..if in fact the FX1 will require them. At this point, based on my research, I don't believe it will, however the wildcard here is the FX1's consistency of focus across the frame. If any spacing is required, I believe it will be minor. Certainly, using a 55mm achromat in front of a 72 or 82mm lens is not ideal, and I'm pretty convinced is the reason for the edge softness experienced by M2 users with the larger lens cams.