Something odd there. I am not liking that it sounds like there is room for forward movement inside the boot.
Please measure your foot using this method:
Kick your heel (barefoot please, no socks) back against a wall. Mark the floor exactly at the tip of your toe (the one that sticks out furthest - which toe this is will vary by rider). Measure from the mark on the floor to the wall. That is your foot length and is the only measurement that you will want to use. Measure in centimeters if possible, but if not, take inches and multiply by 2.54 (example: an 11.25 inch foot x 2.54 = 28.57 centimeters).
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.