While electron–phonon coupling (EPC) provides a well-established framework for understanding conventional superconductors, its role in Fe-based materials, where strong electronic correlations and competing orders are prevalent, remains an open question. Here, we integrate first principles dynamical mean field theory calculations with the epitaxial growth of single-layer FeX (X=Se, S, Te) films on SrTiO3 (001) substrates, which allows us to control the FeX4 tetrahedral angle and electron correlations. Using scanning tunneling spectroscopy, we demonstrate a superconducting dome where the pairing gap peaks at a magic angle of the FeSe4 tetrahedron. Crucially, our calculations show that the electron coupling to the A1g phonon mode is maximized at this magic angle in the FeSe film. Compared with superconductivity in Cs/K doped bilayer FeSe/SrTiO3, our finding demonstrates that the primary boost to superconducting Tc in monolayer FeSe/SrTiO3, arises from intra‑layer correlations that reinforce the EPC within the FeSe film.