Hey Victor, as Andrew stated the gap between the the front and back is ok, as a matter of fact it's suggested. For starters you really don't want the plastic from either the front or back digging into your shoulders. Take a look at other AM builds to get a idea on what kind of gap to look for, there are no specifications. Here's a pic of some recently built armor I did for a fellow garrison member. Your gap doesn't have to be a wide as this however, having elastic sitting on your shoulders is much more forgiving than plastic.