Artificial magnetism in optical frequencies is one of the most intriguing phenomena associated with metamaterials. The Mie resonance of high-index resonators provides an alternative approach to achieving optical magnetism with simple structures. Given the generally moderate refractive index exhibited by available materials at optical frequencies, Mie resonances usually suffer from coupling between the multipole modes, and the corresponding response of the Mie metasurfaces can be analyzed based on the concept of “meta-optics.” Here, we show that the optical magnetism in high-index resonators can be significantly enhanced by adding a highly reflective back mirror to the system. To highlight the transformative ability of this approach for improving meta-optics in the linear and nonlinear regimes, two proof-of-concept demonstrations are presented. Theoretical modeling reveals that low-pump power ultrafast nonlinear optics can be realized in periodic Si nanodisk arrays backed with a gold film, a system supporting guided resonance modes. Moreover, based on the enhanced magnetism of individual high-index resonators, a pair of silicon cuboids is demonstrated as a magnetic antenna for directional excitation of surface plasmon waves. The interference-enhanced magnetism of high-index resonators provides a disruptive technology for enabling meta-optics comprising ultracompact, high-speed, and power-efficient photonic devices.