In this work we studied the influence of three different SiC powder size distributions and the sublimation behavior during physical vapor transport growth of SiC in a 3 inch crystal processing configuration. The evolution of the source material as well as of the crystal growth interface was carried out using in‐site X‐ray computed tomography. Two SiC powders exhibited a single modal D90 size distribution of ca. 50 μm and ca. 200 μm, respectively. In both cases the average SiC powder density was 1.2 g/cm3. The third powder was a mixture of the above mentioned source materials and exhibited a bimodal particle size distribution. The corresponding average SiC powder density was 1.7 g/cm3. In this latter case the in‐itu X‐ray computed tomography study revealed an improved growth interface stability that enabled a much longer crystal growth process. During process time, the sublimation‐recrystallization behavior of the mixed SiC powder showed a much smoother morphology change and slower materials consumption as well as much more stable shape of the growth interface than in the case of the less dense SiC source. By adapting the size distribution of the SiC source material we achieved to significantly enhance stable growth conditions. Copyright © 2018 VBRI Press.