I've got the R1, with Canon 5D and the 8-15mm fisheye.
Trying to shoot a row at 0 degrees, getting the alignment along the horizontal adjusment I've tried it at every point, 16mm, 17mm, 18mm 20mm.
17mm seems to be the sweet spot, at least most of the time. I saw others on this forum also mention around 17 and 18mm to be the best for them.
So how is the R1 designed to take the zenith and nadir? I see the little user guide states to tilt the camera up and down after loosening the knob. Do you also have to slide the pole/tripod a couple of inches as well? I'm a bit lost at that point.