The efficiency of a mode detection array for azimuthal mode decomposition in turbofan nacelle experiments is investigated using numerical acoustic solutions obtained with the finite element code ActranTM. First, steady irrotational inviscid mean flow fields are computed for sideline conditions, with and without an external flow at a Mach number of 0.2. Then, the upstream propagation of duct modes representing fan noise components is performed for three frequencies by solving the Möhring’s equation in the frequency domain with ActranTM using low-memory numerical methods. The acoustic solutions are interpolated to the microphone locations of the mode detection array. In all cases, the azimuthal structure of the interpolated data is obtained using an iterative Bayesian inverse approach, previously developed by the authors. It is compared to a reference one, determined by a duct mode decomposition of the full acoustic solutions considering annular and circular cross-sections. The results provide guidelines for the analysis of future experimental measurements. Indeed, this procedure can be applied to design improved microphone arrays by defining judicious axial and radial positions for azimuthal and radial mode decompositions. Moreover, the approach can determine the optimum azimuthal discretization for azimuthal mode decompositions.