Hey Russell looking good sir. You look to be about the same body type as me. 1-1/2" - 2" gap between the chest and back is good. The overall goal of the armor is to hang on the elastic area however, it won't be perfect, everyone's different.
Have you decided on which type of sections attachment your were planning on going with, wire or snaps? Wire is Canon and a bit more complicated to assemble, snaps easier to work with, and both are Centurion approveable.