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.
^^^^Much of this is great advice. Calling can be somewhat overrated. Highballing ducks is a good start when your spread needs a look. Once they see, running jerk lines with swimmers and feeders creating motion and water movement is all you’ll really need after that. Nothing attracts ducks more than movement. At that point calling isn’t really needed. Regarding calls, I use a KM cut-down keyhole basic. To me it is the ultimate call providing both loud, soft and in between versatility. Easy to blow and makes the most authentic sounds out there in my opinion. Good luck.
