The object of using decoys is to lure duck within range, but not necessarily to get them to pitch into your decoy rig, so if the local geography dictates that your decoys will be afloat further from your hide than you would like, then don’t worry too much.
Try to set out the rig to encourage duck to fly over your hide before, or after, taking a look at the decoys.
Ideally, though, keep the furthest decoys at a maximum of 40 yards. When shooting on flooded washes I group decoys in clumps of three or four, with spaces in between, the closest being about 15 yards from the hide.
Remember that a duck 40 yards away will be almost invisible when it is nearly dark.
I also like to position two or three decoys behind me, possibly floating in a creek or dyke.