Optical tomography of small tissue volumes, as they are encountered in rodent or finger imaging, holds great promise as the signal-to-noise levels are usually high and the spatial resolutions are much better than that of large imaging domains. To accurately model the light propagation in these small domains, radiative transport equations have to be solved directly. In the study at hand, we use the frequency-domain equation of radiative transfer (ERT) to perform a sensitivity study. We determine optimal source-modulation frequencies for which variations in optical properties, size, and location of a tissue inhomogeneity lead to maximal changes in the amplitude and phase of the measured signal. These results will be useful in designed experiments and optical tomographic imaging system.