Series of experimental pinhole topographs are presented, which were taken by exciting a perfect, plane-parallel crystal plate in the three-beam case of diffraction. These images depict the energy flow inside the crystal. Therefore, modifications of the energy flow in the three-beam cases can be made visible directly. In this paper we investigate the effects of changing the coupling strength or the triplet phase between the two primary reflections. The experimental results are compared with simulations of the recorded intensity distributions and discussed with reference to the course of the dispersion surface.