Recently, the significant peak effect was observed in the CeO2 doped Y–Ba–Cu–O (YBCO) bulk materials grown using the infiltration growth (IG) method. The peak effect was attributed to the compositional fluctuations in the matrix, (Y,Sm)BCO. However, it was found that the peak effect was strongly spatially dependent. The inductively coupled plasma mass spectrometry (ICP-MS) results show that the concentration of Sm ranges from 5.8 × 10−2 to 7.0 × 10−3 wt% within the bulk. Notably, the peak effect is only observed in specimens where the concentration of Sm is higher than 1.5 × 10−2 wt%. The spatial distribution of Sm dissolved from the SmBCO seed is the result of the way in which the liquid (BaCuO2 and CuO) flows during the melting process of the IG technique. To suppress the variation in the composition, nano-sized Sm2O3 particles are added to the precursor powders in this study. Microstructural analysis demonstrates that with the addition of nano-sized Sm2O3, the concentration of Sm can be enhanced to be higher than 1.5 × 10−2 wt% within the bulk. Therefore, the peak effect can be observed throughout the bulk material. Besides, more symmetrical trapped magnetic field profiles can be obtained.