An instrument includes a handle portion, an actuator, a shaft, a rigid member, and an angular control mechanism. The shaft has a proximal end and a distal end with an electrode region, and a flexible region in between. Moving the actuator causes portions of the flexible region distal of a pivot region to bend such that an angular orientation and a radial offset of the electrode region reach a maximum angular orientation and a maximum radial offset, respectively, when the actuator reaches the end position. A distal portion of the rigid member defines the pivot region. Moving the rigid member along the shaft causes the pivot region to translate. The maximum radial offset varies depending on the position of the pivot region. The angular control mechanism is configured to control the angular orientation such that the maximum angular orientation is same regardless of the position of the rigid member.
