This work presents a magnetic near field-based RFID system in which a miniaturized RFID chipless tag of 1.65 mm2 is detected by two RFID readers (#Reader 1 and #Reader 2) of different sensitivity. The two readers are 7.5x7.5 mm2 tunable segmented square loop antennas working in UHF band. However, #Reader 2 presents a better impedance matching and a finer frequency tunability than #Reader 1. Measurements were post-processed using frequency sweep envelope (FSE) method and the RFID chipless tag was detected at a maximum distance of 6.5 mm with #Reader 1 and at 11 mm in the case of #Reader 2. In this way, it is proved that a RFID reader with higher sensitivity in frequency and magnitude allows to detect RFID chipless tags at longer distances.