I do realize you have much more experience than I do in this. I was just trying to clear things up for OP. Expansion joints as name indicates allows for the entire floor to expand by creating a space for it to do so. Foam or some medium is placed around the perimeter where the floor abuts the walls. Otherwise it will crack upon expansion. Control joints (in the middle of the floor) create a weak spot such that when the floor does crack it does so in the controlled location.
'97 Prostar 190 - LT-1
Prior boats - 2009 X14, 2008 X14, 2005 197, 1988 Tristar 190, 1989 Prostar.