I have no idea if this would work for ducks but I have used this technique for other animals that seemed skittish of people or being handled.
Put a blanket down on the ground. BRing a book or magazine or music to listen to. Bring a treat that you have lots of.
Sit on the blanket and ignore the animal(s). Wait for them to come up to you to investigate. When they come over to investigate, reward them with treats. Each time you do it, the animals have to come a bit closer or tolerate a bit more handling to get the treat.
Repeat indefinitely until they no longer seem skittish.
This won't immediately help with the herding but it may help build a closer bond with the ducks which may,in turn lead to easier herding.
I talk to my ducks while I'm herding them. This helps me keep it focused in my mind's eye where i want them to go and hopefully helps them figure out i want them to go to a specific spot.
When I first started herding them, I had two hiking poles to serve as arm extensions because i'm short and dumpy :) I didn't need them but they may help you extend the "barrier" far enough so they can see the boundaries they need to stay between.
I use my arms to form a cone around shape and try to keep the ducks inside the cone. This may mean micromanaging a single duck that doesn't go where i need her to go.
It may be easier to focus on getting just one to go where you want. When all else fails for me ( because frogs are yummy!) if i can get one to the right spot the other three come fwap-running to the pen because they don't want to be separated.
I know it's anxiety-inducing and frustrating when they need to be in safe place NOW. I have to stay centered, zen like, in the zone... basically focused on getting from point A to point B with no rush.
I wish I had more to offer.
PS- I sometimes have the opposite problem. Im standing right next to my girls, inches away, and they won't move forward.. because they know I'm too soft to threaten them. I use a soft "tshhhh" noise to let them know i really do mean move it.