Lens based Microwave Kinetic Inductance Detectors combined with distributed absorbers are one of the main candidates for large format, extremely sensitive detector systems for Far Infrared Astronomy. In this paper, the optimal design of integrated dielectric lenses, based on the response of the distributed absorber to incident plane waves, is studied. For the analysis, two efficiency terms are defined, namely spectral and spillover efficiencies, decomposing the effect of the absorber’s response to incident plane waves from that of its physical dimensions, on the total power captured by the detector system. Linearly polarized absorbers, made of Aluminium strips are considered as an indicative absorber geometry, with or without a quarter-wavelength backing reflector.