From bouncerific bonus 1:
Now for the important part: Placement.
You want the tele destination to be exactly where you want to teleport to in relation to the
origin of the teleporter. And the size of the teleporter defines the range you can be teleported to.
Or in english:
Cut the teleporter to the exact size of the hallway it's in, then put the center of the feet of the teleport destination at exactly the same position as the origin of the teleporter in the new hallway.
So if you have a 512x512 hallway you'd want to put the teleport destination at 256x256 assuming a centered origin.
If you want something like bonus 2 on bouncerific where you have 1 teleport and 1 destination you need to resize the teleporter to redefine where you're able to fall.