That was my first stumbling block in my build. I was using the pictures in the armor build tutorial and actually counted the number of notches that were present on the chest plate and then SECURELY glued them down so I don't think they are getting moved. It didn't give me much wiggle room when it came to attaching the straps to the back plate. I have however, noticed that some seem down farther than others depending on the picture you look at, like the one of Luke...
Thank for that picture, I can't get into the FISD tutorial forum for the picture I used, but mine have the same number of slats or notches as in this picture.
Thanks for the other tips on the build everyone!