I have a britax marathon, installed by a professional installer. My daughter perpetually seems to outgrow the height of the straps before they can be anywhere close to tight. The installer seemed a little concerned, but I don't think he knew what to do about it either. Even with the straps tightened down all the way I can still comfortably fit a hand between the chest piece and her body. Anyone else have this problem, or is it just me?