The 2-1-1 configuration you've seen recently on some UP potash trains through Spokane is not exactly an experiment. It's what happens when CP doesn't have time to reconfigure the power before handing it off at the border.

Normal CP practice has been 2-1-1. Back when we used to see potash loads come south with two units mid-train, that was because CP was moving the rear single DPU up to the middle, at UP's request. But the hassle of having to cut out the mid-train power at Hinkle eventually led UP to ask CP to move the middle DPU back to join the rear DPU before bringing such trains into Eastport. Much easier to simply cut off the rear pair at Hinkle now. Last couple of potash loads past my house have had both DPUs on the rear.

Back when the CEFX SD9043MACs first worked here, they were using a single DPU mid-train on some of the grain trains out of Eastport. Now, standard set-up on UP grain through here is single DPU on the rear. The oddity is when an empty UP train comes back north with the DPU still on the rear, the same way BNSF and MRL handle many of their empty grain and coal trains.