In this paper, we present a method to optimize the attainable moment set (AMS) to increase control authority for electrical vertical-take-off-landing vehicles (eVTOLs). As opposed to 3D AMS for conventional airplanes, hover control of eVTOLs requires vertical thrust produced by the powered lift system in addition to three moments. The limits of the moments and vertical thrust are coupled due to input saturation, and as a result, the concept of traditional AMS is extended to 4D Generalized Moment Set to account for this coupling effect. Given a required moment set (RMS) derived from system requirements, the optimization is formulated as a 4D convex polytope coverage problem, i.e., the AMS coverage over the RMS, such that the system's available control authority is maximized to fulfill the prescribed requirements. The optimization accounts for not only nominal flight, but also for one critical engine inoperative situation. To test the method, it is applied to an eVTOL with 8 rotors to optimize for the rotors’ orientation w.r.t the body axis. Results indicate highly improved coverage of the RMS for both failure-free and one engine inoperative situations. Closed-loop simulation tests are performed for both optimal and non-optimal configurations to further validate the results.