×I put my first decoy on (19,16), sword NW

×DROD number: 688
20th Skywatcher!

If you want to play KDD AE in DROD 5.0

If you want Neather sprites

DROD Statistics: (rooms/secrets/challenges)

Official Holds Total Room Count (without KDD AE): 4197
Official Holds Total Secret Room Count: 357
Official Holds Challenges: 344

Nice links:
FlashDROD
Levelmaps
Challenges
Hall of Legendary Smitemasters
Idea Generator
Room Search
Architects Edition

×Just kill the first decoy! Don't be squeemish

×The second decoy has two purposes:
-killing the first decoy
-using its sword to scare the goblin further east so it gets attracted to the third decoy

The key point here is that you want the goblin to be attracted to the third decoy and not the second. You also want to place the third decoy as far to the east as possible.

When a monster is between two decoys, it moves towards the closest one. If the distance is the same, it moves towards the one that was placed more recently. (Specifically, the one that's later in the movement order, even though decoys don't actually move.)

So if you were placing a decoy further down the corridor and then killing the first decoy, then you would either lose a tile or have the goblin get attracted to the decoy that made the kill rather than the one further down. I don't know if this is what you did, but it might explain your confusion.

If you need additional help, the decoy that kills the first decoy should be facing east. That's what my demo did, anyway.