Accurate knowledge of the dielectric properties of biological tissues is necessary for the design and development of electromagnetic medical technologies; these properties quantify the accuracy and efficacy of system operations. Despite the pressing need, the dielectric properties reported in the literature have suffered from inconsistencies mainly attributed to differences in measurement procedures. In this work, a key source of uncertainty, heterogeneous tissue composition within the sensing region of the dielectric probe, is investigated for biological samples composed of porcine muscle and fat. In particular, the contribution of tissues within the sensing depth to measured dielectric data is quantified and the assumption of equal impact of all tissues within the sensing depth is examined. This study demonstrates quantitatively that tissues at different depths below the measurement site do not contribute proportionally to the measured properties, thus suggesting that new analysis methods need to be developed to account for heterogeneous tissue samples in dielectric measurement data. This improved understanding of how heterogeneous tissues within the sensing region affect dielectric measurements facilitates future studies to reduce uncertainty and improve the quality of collected dielectric data of biological tissues.