There has been a recent study which showed that metal-etched dielectric layers placed over Phased Array Feeds (PAFs) comprising open-ended waveguides can serve as effective impedance-matching structures . That work, however, only considered the case of prime-focus single-beam reflectors, and did not examine the layers' effects on the aperture efficiency and its contributions of the entire PAF-fed reflector antenna. This motivates further investigations of such dielectric layers over PAFs. As an example, the present paper studies an array comprising open-ended sidewall-loaded hard rectangular waveguides such as considered in  and shown in Fig. 1. We demonstrate that over a large scan range of multiple beams, both the decoupling efficiency of the PAFs (the parameters which can be used to quantify the overall power losses due to reflection and mutual coupling effects of the array ) and the illumination efficiency of the reflector can be significantly improved.