Jurgen,
Yes indeed, and that was one of the points! With 20mm of fall, I am very near the usable edge of the IC, and that edge IS at the bottom of the image and why I cropped form there to show how good that "bad" area can be!
Re vignetting, the 70 does have some, but less than the shorter lenses; less extreme light falloff is a side advantage of having a retro-focus design lens over a symmetrical design lens. In the case of the 70, the IC essentially remains usably sharp to about the last 2mm before it cuts off (vignettes totally black), and this area is maybe 1 stop lower than center field, easily corrected in the LCC. Interestingly, with the 23 HR the usable resolution is also very close to the cutoff point, giving you about 4mm rise/fall and 2mm shift capability with the 23 on the IQ180 sensor -- but that lens has serious enough light falloff you need a CF at all times. My 40 HR gets unusable resolution-wise maybe 6 or 8mm before it cuts completely off, and that point is about 2 stops lower than center field -- hence a CF is probably a good idea, but so far for me, C1's LCC has handled it incredibly well and I have not felt the need for a dedicated CF on the 40. Lastly, sometimes the extra illumination in an otherwise useless resolution part of the circle is an advantage as it may be in a non-critical part of the frame; and thus gives you some extra shift room for composing purposes... Make sense?
Just for fun, here is another crop from the extreme lower LH side of the frame above. Note that you can start to see the resolution "smearing" as it approaches the last usable limits of the IC. Note that I cannot define the exact point where resolution becomes unusable, as it will vary from user to user and even image to image. For me, this is still usable resolution for an extreme corner even if I printed this to 50", and I would probably even accept less in an image like this. However, if this were at the main foreground rock above, I would not be satisfied except for some quite smaller print sizes: