This work originates from the realization that, in a transformed impedance thru-reflect-line (TRL) calibration, the sensitivity to random measurement errors is affected by impedance discrepancies between the impedance transformer and the device-under-test (DUT). Through a thorough exploration that includes theoretical analysis, simulations and TRL measurements, this study establishes that the accuracy of de-embedding operations on a transformed impedance medium is intricately tied to the difference between the Thevenin impedance seen from the DUT-side of the launcher and the DUT impedance. A noteworthy finding is that minimizing this difference enhances the resilience of the de-embedding process against random measurement errors, being advantageous for precision modeling techniques, and demonstrating the importance of considering those concepts when designing an access structure to a DUT.