Spent the day at a instructor's clinic. One of the 'drills" we did was putting on your boots. It went like this: Slide the boot on. Buckle the two lower buckles. Push the tongue down into the boot until you feel its pressure on the top of your foot/ankle. Then wrap the power strap around the inner boot and tongue ...keeping it completely inside the shell. ("if you can't do this you'll eventually want a different boot") "Powerstap is there to eliminate any movement between your shin and the inner boot tongue".
"This will not effect the stiffness of your boot." Flex the boot several times driving the tongue against your foot and forcing your heel back into the boot. Once satisfied buckle the top two buckles of your boot. And you are good to go.
Shell fit? Less than a finger extra in shell length. Punch, grind and mold until your entire foot is held with the same pressure and movement as a firm, but shy of a painful hand shake.