OK Online I tried the following combinations with the IAD-FAT leg.
FAT-SEA prices at 50k
FAT-BOI prices at 50k
FAT-ORD prices at 25k
FAT-MSP prices at 25k
Obvisously they have some mechanism that is pricing the tickets higher based on the long open jaw.
All of my FAT connections were thru SLC. The thing that does not make a lot of sense, is the SLC-MSP and SLC-ORD flights would cost DL more, than if I took the SEA routing.
Amazingly, there were loads (i mean loads) of date in late September and early October that had Skysaver availability!
I'd give it a try on the phone.
MO