The problem with adding the fees on to a cod is that the fees increase as the amount rises. Because postage is a percentage of the payment, not a consideration of the item.
If you type in a cod of 14k, it is charging you 710 postage. So then you bump the cod to 14,710 so the buyer covers the postage. But doing that causes postage to increase to 745. Bump the cod again to 14,745, and postage increases again.
Of course, in my opinion only whiny OCD tedious pains in the arse really give a carp about a few hundred coins. For some reason those people are scrounging those few coins because they have issues making gold, and are poor.