Tools for electromagnetic simulation make EM computations down to millimeter wavelength possible from large complex targets and their environments. In this paper, we present how we add localized support for N-OP, most useful for cavities and other complex objects subject to multiple reflections, to our shooting-and-bouncing-ray SE-RAY-EM software. This extension is made with the Iterative Physical Optics (IPO) method, which we improve to make it suitable for use in intensive EM simulation of large scale scenes with localized N-OP bounces accuracy. As we present, this requires a generalization in materials, numerical robustness, computational efficiency and a more precise hybridization method than existing work.