Orbital angular momentum (OAM) based communication systems utilize the orthogonality of OAM states to multiplex communication channels. A potentially efficient OAM based communication system may employ flanged circular cylindrical waveguides for transmission, given the natural OAM states of the waveguide modes. The electromagnetic field launched by a propagating waveguide mode propagates a vortex beam with an amplitude null along its propagation axis. Receivers optimally should be placed along the direction of the radiation main lobe of the launcher. In this work, we study the relationship between the flange angle of the launcher and the angle of maximum gain in the main lobe of the radiation for four different OAM states. We demonstrate that OAM may have a significant effect on the sensitivity of the angle of maximum gain to variation in the flange angle. The presented results are confirmed using full-wave simulation.