Does input impedance of an isolation amplifier or a transformer have impact on common mode to differential mode conversion?
If Rin is low in value, the voltages at the input terminals of the isolation amplifier will be "dragged" closer to each other compared to the scenario when Rin is high in value. This means that Rin's value does affect the conversion of common mode to differential mode signals. If you take it to extremes, if Rin is zero there can be no differential voltage.