The Greenlee Circuit Tracer that I use has an adjustable sensitivity on it, so if you have it cranked up on high sensitivity, then yes, you will pick up the signal on the entire phase of the panel that the signaling circuit is connected to. If you adjust the sensitivity to the low end, it is pretty effective in isolating the specific circuit. My only thought on this is that you have the lowest resistance on the actual circuit in question as the signal is coming in on the conductor of the circuit and connecting to the breaker, in comparision, even though the signal is still feeding back through the breaker and into that phase of the panel, each time you come to a breaker that is on that phase, the signal will be weaker because of the resistance that is added both by the breaker that is connected to the actual circuit that you are tracing, as well as the other breaker that you are checking at that point.