I triple-checked the installation of the Shiftmate, but did not bench test the SRAM RD. I'm going to look at the RD more closely regarding spring tension, but setting that aside I've only 6" or so between the frame cable stop and the RD cable stop and it's not a straight shot. So with the ferrules undersized compared to the Shiftmate features I don't have good alignment of the cable with the Shiftmate. And Jagwire cable is pretty stiff. I can see the angle between the Shiftmate and ferrule change as the cable tension is increasing which doesn't seem like a good thing.

Always good to remind folks of the small pulley/big pulley sequence; when I first installed the Shimano configuration I didn't read the directions too closely and neglected to reverse the pulley