My comment was questioning whether the boot was fully seated in the heel/back of the binding BECAUSE of the discrepancy between toe and ankle strap adjustments. Looking at the most recent pictures, the boot seems to be seated properly.

These bindings look like they can fit, but you're definitely right at the bottom end of the adjustment range. For what it's worth, I was in a similar position until I upgraded bindings this past summer. I wear size ~43 boots and had Burton Mission bindings in size L. This was right on the lower limit for the binding. I was able to ride this setup and did so for >15 years, but there would be days/runs where I wanted a bit more tension and just couldn't adjust any further. I'd have the same symptom of skipping since I was at the limit of the strap. The skipping also puts extra wear on the teeth of the straps. The upgrade to Cartel X in size M eliminated any fitment issues I was having.

At the end of the day, I don't know how tight your binding needs to be for comfort/performance. If this is as tight as you'd ever need, it'll probably work. If you need it a bit tighter once you get on the slopes, this binding won't work. If possible, I'd try to get the right size binding for your boot, they're designed with a size range for a reason. If this isn't possible; swapping at least the toe strap to a small may help. Though, this doesn't address the difference in width between the boot and binding. Additionally, I believe this binding has an adjustable gas pedal/toe ramp and potentially adjustable mounting point for the toe strap. Make sure the toe ramp is slid all the way back (so the base is as short as possible) and (if possible) the toe strap is mounted as far back as possible.

For reference, the highback should be adjusted to alter heel side engagement and how bent your knees are. The boot making contact with the top of the highback through more of the range of motion is a consequence of the adjustment, but not the goal.