The role of magnetic proximity on topological surface states (TSSs) and spin-charge conversion efficiency is studied in Fe/ topological Dirac Semimetal α-Sn heterostructures. As α-Sn thickness increases (9–35 nm), the damping constant of Fe peaks at 25 nm and then decreases. Theoretical modeling links this to long-range magnetic proximity effects (MPE) that suppress TSSs at the Fe/α-Sn interface while opening an exchange gap at the opposite interface. At 25 nm, we achieve an inverse Edelstein length of -3.1 ± 1.0 nm, one of the highest value at room temperature, highlighting MPE’s importance in spintronics.