Before performing electromagnetic interference (EMI) measurement tests in the frequency range below 30 MHz, the test site must be evaluated by normalized site insertion loss (NSIL) using a pair of loop antennas. The site insertion loss measurements are performed with three arrangements of loop antennas to measure three-axis components of magnetic fields in the near-field regions. In this paper, it is shown that the locations of the feed gaps on the loop antenna elements change the values of the SIL. The preferable locations of the feed gaps are proposed to perform the NSIL measurements with the measurement results in a semi-anechoic chamber.