I have had both a 1440 and a 1660 that literally windrows grain over the top sieve when cutting on steep terraces.
I've had the dealer out and they haven't been able to solve it but says they don't have that problem with the 80 series.
I've tried different sieves, have the new type fan, and it just seems to me like all the fodder comes to the downside of the sieves and the wind blows thru the empty upside, therefore walking the grain right out the corner of the downsize sieve. I've been told to run the right side down.
The sieves have divider fins on them. Anyone that has experienced this and corrected it, I would appreciate it if you would let me know. Located in Kansas.