This study presents a novel approach to analyzing high-energy radio-absorbing composites (HRCs) by combining computational modeling and experimental measurements of temperature field distribution under microwave irradiation using a waveguide-based setup. Unlike previous studies that mainly focus on nanofillers or bulk dielectric properties, our work investigates the thermal response of a composite with a single macroscopic SiC sphere (d = 20 mm), embedded in epoxy resin (ED-20) and fluoroplastic (PTFE) matrices, both as an individual sphere and in grouped configurations. This setup enables direct observation and modeling of localized heat accumulation and dissipation pathways. Temperature distributions were examined in filler and at a boundary of filler-matrix at various distances from the filler–matrix interface under different power levels and thermal boundary conditions in ED-20 and PTFE. The results demonstrate that the ED-20 matrix with a 20 mm SiC filler offers an optimal balance between microwave energy absorption and thermal stability. However, at power inputs above 400 W and heating rates exceeding 10 °C/s, signs of thermal degradation and matrix damage were observed. These findings provide new insights for the design of thermally robust, structurally optimized HRCs with tunable electromagnetic performance.