We investigate the plasmonic coupling of metallic nanoparticles with continuous metal films by studying the effect of particle-to-film distance, cavity geometry and particle size. To efficiently screen these parameters, we fabricated a particle-to-film coupled functional nanostructure for which particle size and distance vary. We use gold-core/poly(N-isopropylacrylamide)-shell (Au-PNIPAM) nanoparticles to self-assemble a monolayer of well-separated plasmonic particles, introduce a gradient in nanoparticle size by an overgrowth process and finally add a coupling metal film by evaporation. These assemblies are characterized using surface probing and optical methods to show localized magnetic and electric field enhancement. The results are in excellent agreement with finite-difference time-domain (FDTD) modelling methods and calculations of the effective permeability and permittivity. Finally, we provide a proof of concept for dynamic tuning of the cavity size by swelling of the hydrogel layer. Thus, the tunability of the coupled resonance and the macroscopic self-assembly technique provides access to a cost-efficient library for magnetic and electric resonances.