Advice on getting ducks to finish

So this past Friday I found a large flooded lake bottom grown up with willows, buckbrush and lots of vegetation. It was broken up with pockets of water and beaver channels. It also had hundreds of mallards in it. Saturday I hunted it for the 2nd split opener (in OK) expecting to have a quick limit - boy was I mistaken.

I hunted with 2 other experienced hunters. We were well covered and were hunting over a spread that consisted of 12 mallard decoys (4 active, 4 feeders, 4 sleepers), 4 gadwall on a jerk string, and a single mojo. All morning an almost identical scenario played out regardless of whether we used the mojo or not, where we were located (we moved thinking that was the problem and it didn't help), and whether or not I touched the jerk string.

90% of the workable birds would come in, circle, respond well to light calling when flying away, continue to circle numerous times and then finally leave. They didn't land anywhere close by and other than the few flocks I know flared from us being dumb, they didn't seem to flare - just decided not to land. The ones we did kill were really just the few birds whose circles were low enough and directly overhead.

Furthermore, they almost seemed to disregard the decoys. They would circle over specific openings in the water or over us (presumably due to the calling), but really didn't focus on the decoys much at all.

Any advice on what we could do differently? Way more decoys? No decoys? Different decoys? FWIW, almost all of the 150-200 birds we saw that worked were mallards.

ETA: picture for your troubles: