PETER THEOBALD says: The whole purpose in using decoys is to deceive a truly wild bird and draw it within range of your hide.
If you are really clever, you can manoeuvre them in such a way as to make your shots fairly straightforward.
Sometimes you can do this with six decoys, other times it may take 76.
The point I am making is, once you have got the birds responding to your satisfaction, there is no point adding further decoys to the pattern.
Indeed it can be counter productive, as the constant toing and froing from the hide can break the flightline, and also there is the danger of not leaving any gaps in the pattern for incoming birds to head for, and they turn off out of range.