I'm not sure about harvested corn in home storage, but I have seen numbers on these:
Wet by products, 5-6% shrink in a commodity shed, 10-12% shrink from a concrete pad and no roof, 15-20% shrink when stored on dirt. (These assume you are feeding it fast enough to stay ahead of spoilage).
Dry by products, 2-3% shrink in a bin,  3-5% shrink in a commodity bay, 8-10% shrink in an outside pile.
Corn silage in a bunker, 5% shrink with inoculant, bunker cover, and excellent face management; 15-20% shrink with none of those.
Processing corn on farm, 3-5% shrink.