An electrical ground (36) of an RF impedance matching network (33) is connected to a connection area (50) on the grounded chamber cover (18) of a plasma chamber. The connection area is offset away from the center of the chamber cover toward a workpiece passageway (20). Alternatively, an RF power supply (30) has an electrically grounded output (32) that is connected to a connection area (52) on the chamber cover having such offset. Alternatively, an RF transmission line (37) has an electrically grounded conductor (39) that is connected between a grounded output of an RF power supply and a connection area (52) on the chamber cover having such offset.