Precise measurements of the surface resistance of high temperature superconducting (HTS) thin films using transmission mode dielectric resonators requires accurate knowledge of the unloaded Q factor (Qo). So far, the most accurate method of Qo determination for transmission mode resonators is the transmission mode Q factor (TMQF) technique based on the processing of S-parameters (S21, S11, S22). The technique accounts for parasitic effects including noise, crosstalk, coupling reactance and coupling losses but does not yet take into account the impedance mismatch between the test ports of the vector network analyzer and the inputs to the resonator. Discrepancies between measured and ideal S-parameters due to the mismatch lead to inaccuracies in coupling coefficient computations. This causes undesirable error in the calculated Qo. We present measurements of Qo obtained using the TMQF technique for mismatched and matched connections between the test ports of the vector network analyzer and the inputs to the dielectric resonator. These results are compared with values obtained using the traditional insertion loss method.