Hunt only in the afternoon. Stay out of the woods and only hunt the field when the wind is blowing from the woods into the field. Sounds to me like they be bedding in the woods. Spread the corn thin on the edge of the field. Make sure your travel path is along the edge of the field.
I had the same thing happen to me a couple of years ago on a small patch. I was sitting up a stand bow hunting one ofternoon and heard a deer get up right behind me. I figured out that the reason I wasnt seeing anything is that they were bedding close to where I was parking my truck and watching me walk in. The first two nights of entering the property from a different direction produced two nice bucks. If you are seeing sign then there are deer. Just outsmart them.
Good luck