Supported lipid bilayers (SLBs) are cell–membrane-mimicking platforms of varying biological complexity, that can be formed on solid surfaces and used to characterise the properties of the plasma membrane or to study membrane interactions at the molecular level. The incorporation of microfabricated electrodes and transistors has allowed for their electrochemical characterisation using techniques such as Electrochemical Impedance Spectroscopy (EIS) and transistor-based impedance spectroscopy. In this work, we combine experimental data with numerical simulation to explore the relationship between changes in SLB quality and impedance output, delving into a deeper understanding of the impedance profiles of devices with and without SLB, as well as extracted parameters such as membrane resistance (R_m). We extrapolate this approach to investigate the relationship between microelectrode area and sensor sensitivity to changes in SLB state, towards rational device design. We highlight the trend of electrode size (polymer volume) required for sensing bilayer presence as well as the dependence of the electrode sensitivity to the SLB capacitance and resistance. Finally, we illustrate how our flexible approach of including electrode and transistor measurements to amalgamate characteristic impedance spectra of transistors, overcomes the problem of low frequency noise and errors seen with traditional EIS.