QTR-Quadtone RIP

Here's an update. I printed a 16x30 on Photorag original, same
settings as described in my intro post (but with sheet feed, manually
cut), and I got a 16" measured height on both short sides of the
print, but lost 1/32 on one 30" side, and lost 1/4" on the other 30"
side. This hardly even seems possible, but it's happening. When
mounting and matting, I can see the obvious sweep of the image
shortening. This is baffling me and pissing me off. 

Any ideas? Thank you. 

Michael Gordon