Microwave thermal ablation is an electromagnetic-based technique for treating malignant tissue. However, the success of such treatment highly depends on the design of the ablation antenna, it's positioning in the targeted tissue and the matching of the antenna into the tissue. The common parameter on which all three conditions depend are the dielectric properties of the tissue. Therefore, to improve the ablation technique it would be beneficiary to develop a methodology for in-situ real-time dielectric spectroscopy with the ablation antenna itself. Until now, some studies dealing with this type of measurements have been published, but further analysis of the factors influencing the measurements need to be performed. In this work, the sensitivity of dielectric spectroscopy with asymmetric dipole applicators operating at 2.45 and 5.8 GHz in respect to their immersion depth into the tissue and the longitudinal dimension of the tissue was studied numerically.