yu, if I understand correctly, the measured impedance is roughly double what is desired.
Components that most affect impedance are the circuit’s cable size and length, and serving transformer size {impedance.} Each would effect voltage drop on a circuit.
The only solutions I can imagine are 1.) increasing the size or cross-sectional area of the cables, [likely least expensive, but with a potentially limited improvement] 2.) shortening the circuit length [probably not practical] or 3.) installing a larger [lower-impedance/expensive] serving transformer. These three items are probably at least 90% of what effects source impedance on a branch circuit or feeder.
Tests to determine the change {or improvement} from cable replacement may be to carefully apply the instrument at the feeder level if the circuit of interest is indeed a branch circuit, and then at the serving transformer’s secondary terminals.
I hope that answers your question or confirms your suspicions.
