No, the back plate for 880K-knob trim is the same as for 373L-lever trim. Since 373L is a narrow style trim it require to use the 889 cover plate with this trim.
If mechanism cover plate causes the EL solenoid to drop when slid over the solenoid, the solenoid plunger requires adjustment. You must lengthen the rod by turning the hex nut in front of the plun...