Sorry but you can't raise the cover plate without trimming it : you can put washers/spacers under the 2 bolt down on the left ramp, but the top one and the one on the top right of the ramp cant be installed, the cover is inserted under the surrounding plastics.
Also, I have issues with my TK Lock as well, and I think the diverter is not closing fast enough when the balls crosses the optos.
I have tried everything, the checklist, the coil settings, the game pitch, and most of the time the ball gets pinched by the diverter and is sent backward, with a 75% SDTM chance.
Really annoying.