I wear a size 12 K2 Raider Boa boot. I'm size 12 in shoes, so i figured boot sizing can't be too off. I have L/XL union forces and before them i had M/L union forces. I wear them as a cap strap, not over-the-toe. I've had the same issue with both bindings. The toe strap digs in to my boot where the ladder is. Its not nearly as bad on my L/XL, but it just gets painful after riding for a few hours when you feel the strap up against your pinky toe. And my heel also moves a little in the boots, which i don't know how to prevent.
I tried adjusting the toe strap on the bindings, but then the hole in the toe straps is off centered and doesn't fit the boot right.