Interesting. But, really, under mama, the eggs are not really flat on their sides, are they? Mine, with the straw or hay or whatever settle with the pointy end slanted down and kind of "reclining". I thought that was the reason for the shape of the egg to begin with, and the reason for needing the nesting material. So, naturally, they are really neither straight up nor lieing flat on their sides.
I would also think the nesting material would cushion the unhatched eggs and also help keep them stable while the hatched chicks are moving around