I have killed several mature does with a doe decoy. They hate it, meaning their bow up like a mad dog and will be so tore up about a strange doe being around that I believe I could have done jumping jacks in the treestand and they would have never noticed me. First time I ever used a decoy, used as a doe, I was still climbing tree, only about 10' up. Heard something and looked and a group of deer was coming, no headgear, and I was mad because my bow was on the ground and the direction they were coming I wasn't sure they would see the decoy before me. They did see the decoy and the biggest doe in the bunch went ballistic. Her neck hair raised up, ears laid back and she was intent. Decoy was only 15 yards from the tree. I pulled my bow up, knocked an arrow and after watching the momma doe do her best to intimidate the decoy for several minutes, I shot her. She went about 50 yards and fell over. It has happened several times. I have rarely seen deer spook from a decoy as much as they don't pay any attention to it at times.
Took my brother to a large bean field one year to try bowhunting it, lots of deer using it. The season before, in 11 evenings, we killed close to 30 does out of it late in the season. I told him I was going to put the decoy on the edge and we could climb a tree either side of it. About an hour before dark, a bunch of deer came out. One large doe did spook from the decoy. She would stand about 100 yards out and blow at the decoy then she would run to several hundred yards out and blow, then came back to about 100 yards and blow. She did this til dark. I was pissed, just wanted to kill a doe. My brother is laughing and thinking the whole evening was done, I did to. This deer was tore up. Right at dark, I just happened to look behind the decoy and there is a group of does walking right to the decoy, where my brother would have been. I get ready and the lead doe, big one, walked up to the decoy and put her nose right to the tail (I don't put scent on the decoy ever) and I shot her, the whole time the other doe is still blowing like the end of time is coming. When I walk up to my brother he is still laughing and giving me a hard time about the decoy screwing up the evening. Should have seen the look on his face when I told him I shot one with its nose to the tail of the decoy. She didn't go far and was a nice mature doe.
I would be sure and put it in an open area. From my experience, the more open the better.