We investigate the interface coupling between the 2D sine-Gordon equation andthe 2D wave equation in the context of a Josephson window junction using afinite volume numerical method and soliton perturbation theory. The geometry ofthe domain as well as the electrical coupling parameters are considered. Whenthe linear region is located at each end of the nonlinear domain, we derive aneffective 1D model, and using soliton perturbation theory, compute the fixedpoints that can trap either a kink or antikink at an interface between twosine-Gordon media. This approximate analysis is validated by comparing with thesolution of the partial differential equation and describes kink motion in the1D window junction. Using this, we analyze steady state kink motion and derivevalues for the average speed in the 1D and 2D systems. Finally we show howgeometry and the coupling parameters can destabilize kink motion.