This setup is best during the rut. The buck indeed helps "sell" the idea that the doe is in estrous and the buck is on guard.
The more realistic it is the better.
A good rule of thumb is that you want the antlers on your decoy about 10 inches or so less than your goal.
You may want to check this thread out for additional opinions- http://forum.deeranddeerhunting.com/tm.aspx?m=43979