It's not the size of the eggs, it's the size of the hens. So for example if you wanted to make your NN's bigger using Brahmas, you put a NN roo over Brahma hens to get offspring that are closer to Brahma sized. If you did it the other way around all the offspring would be the size of the NN hens.
My Jersey Giants lay smaller eggs, and some of my smallest NN hens lay huge eggs.
My Jersey Giants lay smaller eggs, and some of my smallest NN hens lay huge eggs.