Plasmonic organic hybrid electro/optic modulators are among the most innovative light modulators fully compatible with the silicon photonics platform. In this context, modeling is instrumental to both computer-aided optimization and interpretation of experimental data. Due to the large computational resources required, modeling is usually limited to waveguide simulations. The first aim of this work to investigate an improved, physics-based description of the voltage-dependent electro/optic effect, leading to a multiphysics-augmented model of the modulator cross-section. Targeting the accuracy of full-wave, 3D modeling with moderate computational resources, the paper presents a novel mixed modal-FDTD simulation strategy that allows us to drastically reduce the number and complexity of 3D-FDTD simulations needed to accurately evaluate the modulator response. This framework is demonstrated on a device inspired by the literature.