The design appears to have an exit nozzle area at least equal to that of the inlet. If so, this is sub-optimal from a propulsive efficiency point of view. The cross-sectional area inside is clearly less (mainly due to the engine nacelle), making this a convergent-divergent nozzle, which is desirable only when the flow goes supersonic. For subsonic conditions, a convergent nozzle, with its exit narrower than its intake, is better.<p>See de Piolenc, 'Ducted Fan Design vol. 1.', 2001