There isn't room in the boot - thats why my toes are getting sore from by pushed into front of the boot. I'm 100% sure these boots fit me well as I have spent nearly a decade trying to find a pair that worked for me (I have even worned the same model boot a half-size smaller).
Let's keep the focus on the FLOW bindings. Go back and look at the video I posted... you can see as I tighten the strap (around 45 seconds), the boot no longer slides forward as much... so when the highback flips up, it pushes IN the back of my boot, buckling it a little bit (throughout the video you can see the "imprint" of the highback on the back of my boot). That's what I'm talking about.