A method for reading radio frequency identification (RFID) tags in a portal system defining a boundary which separates a portal zone into a first physical space and a second physical space, comprising: performing a first detection of one or more RFID tags having a predetermined flag state in a portal zone having a predetermined flag set by generating with an RFID portal at first detection intervals at least one first detection RF field, directed toward the first physical space on a first side of the boundary, to excite RFID tags within a first detection proximity to the RFID portal using one of a Session 2 mode and a Session 3 mode, each mode having a long duration session persistence; performing a second detection of the RFID tags in the portal zone which have the predetermined flag set by generating with the RFID portal at second detection intervals at least one second detection RF field, directed toward the second physical space on a second side of the boundary opposed to the first side, to excite RFID tags within a second detection proximity to the RFID portal using one of the Session 2 mode and the Session 3 mode, whereby during the second detection the Session 2 or 3 is used which is not used during the first detection; performing a first sampling of the RFID tags in the portal zone having the predetermined flag set by generating with the RFID portal at first sample cycle intervals at least one first sampling RF field, directed toward the first physical space, to excite the RFID tags within a first sampling proximity to the RFID portal using a Session 0 mode having a minimal duration session persistence which is less than the persistence of the Session 2 mode and the Session 3 mode, the first sampling proximity extending a lesser distance from the RFID portal as compared to the first detection proximity; performing a second sampling of RFID tags in the portal zone having the predetermined flag set by generating with the RFID portal at second sample cycle intervals at least one second sampling RF field, directed toward the second physical space, to excite the RFID tags within a second sampling proximity to the RFID portal using the Session 0 mode, the second sampling proximity extending a lesser distance from the RFID portal as compared to the second detection proximity; and based on the first detection, second detection, first sampling and second sampling, determining an occurrence of at least one of the RFID tags transitioning between the first physical space and the second physical space. performing a first detection of one or more RFID tags having a predetermined flag state in a portal zone having a predetermined flag set by generating with an RFID portal at first detection intervals at least one first detection RF field, directed toward the first physical space on a first side of the boundary, to excite RFID tags within a first detection proximity to the RFID portal using one of a Session 2 mode and a Session 3 mode, each mode having a long duration session persistence; performing a second detection of the RFID tags in the portal zone which have the predetermined flag set by generating with the RFID portal at second detection intervals at least one second detection RF field, directed toward the second physical space on a second side of the boundary opposed to the first side, to excite RFID tags within a second detection proximity to the RFID portal using one of the Session 2 mode and the Session 3 mode, whereby during the second detection the Session 2 or 3 is used which is not used during the first detection; performing a first sampling of the RFID tags in the portal zone having the predetermined flag set by generating with the RFID portal at first sample cycle intervals at least one first sampling RF field, directed toward the first physical space, to excite the RFID tags within a first sampling proximity to the RFID portal using a Session 0 mode having a minimal duration session persistence which is less than the persistence of the Session 2 mode and the Session 3 mode, the first sampling proximity extending a lesser distance from the RFID portal as compared to the first detection proximity; performing a second sampling of RFID tags in the portal zone having the predetermined flag set by generating with the RFID portal at second sample cycle intervals at least one second sampling RF field, directed toward the second physical space, to excite the RFID tags within a second sampling proximity to the RFID portal using the Session 0 mode, the second sampling proximity extending a lesser distance from the RFID portal as compared to the second detection proximity; and based on the first detection, second detection, first sampling and second sampling, determining an occurrence of at least one of the RFID tags transitioning between the first physical space and the second physical space.