I'm not sure which tower the calls node is on but typically you'll only hear LZ Central 1, LZ West 1, etc. if a radio is affiliated with that tower. Some (but not all) communications centers and hospitals will monitor the LZ talkgroups 24/7.
Also, I think I remember reading somewhere that depending on how the SDR is setup on Calls, some transmissions may be missed, especially if there's not a good decode or the transmission was very short.