We provide experimental support for a recent kinetic model study [Phys. Plasmas 32, 062702 (2025)] that unexpectedly reported the insensitivity of a multi-MA pulsed power magneto-inertial confinement fusion target to the final power feed contaminant inventory. We measured a 1% difference between the peak current coupled to the target by a nominal high-inductance inner magnetically-insulated transmission line (MITL) and the peak current coupled to the target by a contaminated inner MITL in 18~MA experiments on the Z Pulsed Power Facility. We contaminated the inner MITL by adding a net 25 layers of atoms to the anode and cathode current-carrying surfaces via self-assembled monolayer formation of octylphosphonic acid (PO${}_3$C${}_8$H${}_{19}$) and verified the contaminant’s presence and behavior via x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and in situ streaked visible spectroscopy. Our findings reinforce the emerging MITL physics description gleaned from recent kinetic simulations, and our efforts provide a method for testing wall contaminant sensitivity that may be adapted for other plasma-facing applications.