Put it in the middle. I find it best to only have a chain dog in the first and last cars, the middle dont really matter.

only if u want that length of train... but yes, it does actually work better to only have 2 dogs on the whole train, the front and the back... stops chain issues...

It was probably just a mistake when putting it together. Don't worry about it though because like Johnny said, you only need it on the first and last.

Just take 2 of the chain dogs out of your phoenix train, and put them in the first and last car of the statix you want to run. Also remove the other chian dogs.. Or you can modify the chain dog by cutting it to look like the Phoenix ones. 

The chain dogs are different on the Phenix then they are from some of the older Statix or Inverted chain dogs.
J>

Take the train in your hand.. Grab a hyper harness.. You want to grab the two middle seat pads and pull upward.. The restraints will pull up from the base of the train.. Once you pull it out you will see how it fits.. Getting them in all you can do is try, basically you put in one side and kindo of bow it up and slide the other side in. 
J>