The linear response conductance coefficients are calculated in the scattering approach at finite frequency, damping and magnetic field for a microstructure in which the reservoirs are modeled as quantum wire leads of infinite length but finite width. Independently of frequency, inelastic scattering causes subbands with large group velocity to contribute more strongly to the conductance than channels of comparable transmission but slower propagation. At finite frequency and magnetic fields, additional correction terms appear, some of which are sensitive to the phase of the S matrix.