Personally I've had more bad luck using decoys than going without with mature birds other than early in the season. The big boys hang up out of range very frequently when they see the decoy, strutting and gobbling until the real hens filter to them and lead them away.

I've had good luck with decoys with 2 year olds and Jakes. If you got a big boy and want to use decoys make sure to include a jake. Later in the season use one in a less aggressive posture. Although I've had some really exciting results by using a Jake and hen in a breeding position.

I like to set up where the terrain is such than when I see the bird it is already in range. It's not always possible but defintely desireable.

Good Luck!