This is going to cover the factors that affect the ability of humans to absorb Iron which isnt quite addressing your question directly but I would rather not speculate about things that I have not researched as thoroughly. Iron bioavailability depends on several factors including what you eat along with the Iron. Citric acid and protein significantly increase the bioavailability of Iron. Plant foods rich in phytate (what plants use to store Phosphorus) bind to and render unavailable metals like Iron, Zinc, Calcium etc but these levels vary significantly between plant food sources. Other metals like Zinc can interfere with Iron bioavailability and vice versa. And normally the body’s ability to absorb Iron is regulated such that Iron is absorbed more efficiently if you are deficient and less efficiently if you have an excess. There are a few disorders that cause this Iron regulation to malfunction either resulting in deficiencies or the complete opposite of this, excessive Iron that starts depositing in organs but with a physiologically “normal” person that regulatory system acts to normalize the amount of Iron absorbed to an extent.