DR-85.
Only call on the corners, let your decoys work. Keep your face in the shadows or behind the blind so they don't see a big moonpie reflection as they commit.
Jerk cord works probably better than a call, all things being equal. And, make sure you have a hole for them to land in your decoys.
Drakes tend to follow the hens in flight. Mergansers fly horizontal - let them pass.
Good Luck.
