If everyone around you is using mallards, pull the mallards .
Try to look different.
Use a haphazard look to your spread
I've come to rely on a jerk cord on public land.
Couple of Canada Geese may help too
I used to hunt with about 15 decoys for a long time and pull good sized groups. I like the idea above of a couple mallards, I've been thinking about that here. Just going with a few good decoys. Sounds dumb but might work.
What type of ducks are you mainly targeting or seeing?
I hunt pressured areas with lots of bird traffic... The hide is huge... Natural cover and low profile... Building a well-concealed house next to open water will not work.
You can go big with large spreads and flight lanes/holes... Or you can go small, with smaller more realistic decoys..... Both have worked for me. Open water a large spread might draw more birds... But they will often fly the edge of those large spreads.
As far as calling... Depends on the species and on the day... If a little calling is not working, I try more... If birds are bouncing off the call, I call less and more subtle. One day birds want to be called at, and one day they don't.... No calling is frequently better than poor calling. (Record yourself and see how you actually sound compared to how you "think" you sound).