Sorry for the delay, we finally found time to look into this. You are right for the 170deg lens. It seems that the lens mount used in production is a bit longer than what we had for our prototypes. I will consult with the factory about that. I am also ordering more of the mounts we had used for prototyping. We can ship one to you if you want (please email us at email@example.com).
I confirm that for the 170deg lens, if you remove the lens mount from the sensor, you need to get very close to the sensor (about 2-3mm from the sensor) to be in focus. The mount is a bit longer than that, so you indeed bottom out with the lens fully screwed in and are still farther than 2-3mm from the sensor. If you need a quick fix, you may want to unscrew the plastic lens mount from the PCB, and then file it down to make it thinner. It looks like it would have to be substantial (take off 4-5mm or so). I would recommend doing that on the rectangular side of the mount (that comes in contact with the PCB) so that you do not compromise the threads on the other side.
We do not see that problem with the 4 other lenses, though, including the 125deg. We can focus all of them no problem as their thread is longer than the thickness of the lens mount (so you can screw them in all the way to touching the sensor).
For close focus, though, you may be better off with a telephoto lens. We have used this one with success (but it is huge, almost as big as the camera, and heavier):
We can get a single keyboard key to occupy the full video frame with this lens.