It doesn't matter where it is located in the control cavity so long as it touches the shielding paint in the cavity (or shielding foil if it has it), and goes over the lip of the recess for the cover plate. It is the electrical contact between the shield in the cavity and the foil on the back of the cover plate. Anywhere is fine so long as it makes contact with the cavity shield and the cover plate. Best location is at a screw hole, that way the pressure of the screw ensures that the cover contacts the foil strip.
Instrument Technician, Toronto