The key to successful growth of high-quality gallium oxide (Ga₂O₃) single crystals by the edge-defined film-fed growth (EFG) method is the stable control of the shoulder, where a symmetrical flow and thermal field is one of the critical factors. This paper combines numerical simulation with experiments, introducing gas intakes at different positions in the insulation device to regulate the convective behavior of the gas within the insulation, thereby avoiding the negative impact of vortices on the thermal field above the mold. The study shows that bottom gas intake significantly enhances the symmetry of the thermal and flow fields near the solid-liquid interface, achieving an appropriate axial temperature gradient of 40 K/mm, and successfully realizing symmetrical shoulder during the crystal growth process. This achievement provides a foundation for the design and optimization of the EFG system for β-Ga₂O₃ single crystal growth.