A conveyor system includes a plurality of antennas proximate a conveyor path of travel that radiate radio frequency signals into a first area and receive responses to radio frequency signals from radio frequency identification tags on items on the conveyor. A detector detects a height of items. A processor receives response signals from the receiver and controls a transmitter to drive respective antennas in a predetermined sequence, associate a response with a first item if the processor receives the response signal while at least a portion of the first item is within a second area that includes at least part of the first area, and based on signals from the detector, eliminate at least one of the plurality of antennas from the predetermined sequence if the height of the first item is below a predetermined threshold.