Partially coherent optical diffraction tomography (PC-ODT) is a labelfree quantitative 3D imaging technique based on the refractive index contrast. It provides fast non-interferometric speckle noise-free imaging compatible with conventional wide-field transmission microscopes, but suffers from two principal inconveniences. One of them is the missing cone problem, which is a common drawback for all tomographic modalities with limited-angle inspection, including interferometric coherent ODT. The second one, considered in this paper, is a nonhomogeneous contrast for different spatial frequency regions. Analyzing the microscope 3D optical transfer functions for various illuminations over the condenser aperture we have found that the Gaussian illumination shape is a proper one. Numerical simulations and experimental results support this finding. A future line in the development of post-deconvolution processing is also discussed.