Position-dependent resistive pulse ($\Delta \mathcal{R}(z)\propto \rho \Omega /A(z{)}^2$)

A small insulating object of excluded volume $\Omega$ perturbs an Ohmic pore most strongly where the pore cross-sectional area $A$ is small. In a local weak-blockage model, replacing a small conducting volume gives the displayed resistance scaling, with a shape-dependent coefficient. At fixed voltage, $\Delta I\simeq -I_0\Delta \mathcal{R}/{\mathcal{R}}_0$. A symmetric pore with narrow ends and a wide middle can therefore resolve two end features in a passage pulse. This is a conditional volume-exclusion model: charged-particle ion transport, surface interactions and bandwidth can change the observed sign, amplitude and shape.