Impossible to perform a direct comparison test, since we can't put out two different spreads in the exact same spot at the exact same time and have birds respond without influence from both spreads. You may believe a few magnum decoys are better, just as I believe many standard decoys are better, based on anecdotal evidence. Neither of us can offer scientific proof; it's just what we think. Look at it this way: does a flock of flying ducks see a spread of a dozen (for example) oversize decoys and think "must be something good there". Or do the birds see a spread of 24 life-size decoys and think "there must be something really good there". In the duck world, numbers tell the story, not size of the birds. Humans see it similarly: when you're scouting, do you determine the best spot for your hunt by the number of birds there, or by the size of the birds there?