fett chest armor gap?

I am about to attempt to attach my armor to the flack vest,is there a certain size gap between the armor or is it just what looks right?

It really depends on which Fett you're doing. Looking at the ESB photos, you'll notice that the armor is attached very close together. ROTJ Fett is a different gap, as well as the AOSW (SE Fett). If you're doing the SE or ROTJ Fett, just look at the respective museum exhibit photos in the gallery, resize the photo to scale it to your armor size, and measure the gaps from your monitor.

As Ponte says, they all differ slightly. Which version of the armor are you working on?

something else to consider with spacing is to make it look proportionate to your body. if you're a barrel chested dude (like me) space them out a little farther, if you're a skinny kid (like jeremy bulloch) you should squeeze them in a little tighter.