Sounds like you have already over hunted it. Geese are smart birds. If they see the same decoys out there all the time in the same setup, they know something isn't right. If they see birds out there at weird times of the day, they get a bad feeling about things.
It sounds like you have a lot of experience with the same birds. If everytime they get up off the roost and skirt your field, you call to them, they don't like it, they get into a routine. Birds know places to ignore, and it sounds like they have kind picked you out.
On the other hand, the field may just have nothing to offer them. If it doesn't have a lot of food present, and other fields are around, they will find a field with alot of dropped corn rather than an empty one.