I performed transfer function measurements from ITMX_TM to DARM under two conditions: with no dewhitening filter and with all three dewhitening filters engaged, while the interferometer was in the PRFPMI_RF_LOCKED state.

Figure 1 shows the comparison between the WF ON and WF OFF cases. The result is consistent with the expected effect from the low-frequency zero/pole, showing approximately a 0.9 dB (~10.9%) difference.