Up until year before last it was 16-18 feet. Last year I tested out a theory that I have and I feel in this area I was correct. We have been hunting the same 1400 + acres for ten years and know the deer pretty well. Once the leaves came down the deer would disappear, because I felt they could see us going up into our stands. I started to only go up about 8-10' and ended up having deer walk right under me, I also had a buck lean up the tree like a dog that had something treed, I feel that in this particular spot this is what happens.
The reason I came up with this was that I could see further in the woods when the leaves come down so why can't deer. Like I said it's just a theory that seemed to have worked for me.