The effect of diffraction, that is the increase in relative proportion of diffracted light compared to non-diffracted light passing through increasingly smaller apertures, is a property of the lens, not the sensor. The sensor simply captures the effect.
Explaining to someone that
"a lens will have an aperture at which it returns maximum sharpness in detail. Larger and smaller apertures will increasingly return less sharp detail" is hardly difficult to grasp, and certainly not 'complex'.
All they need to do is take a series of photos of the same subject at a range of aperture settings and compare the results when viewed at 100% to determine the lens aperture that returns the greatest sharpness. Either that or save themselves the effort and look at the charts on
www.photozone.de like everybody else. Again, hardly rocket science.