Just making sure, but did you adjust the heel hoop to the size 9 setting?
Ya with that boot size you should have the heel cup in the forward most position, which may or may not fix your problem.
Also, I don't think the highback on my Targas are in contact with my boot for the entire length of the highback. It isn't really clear where your gap is, but it sounds like it is at the top of the highback. What forward lean are your highbacks at? It might just be that the angle built into the boots is greater than the default or whatever angle your highbacks are set.
Is the gap equal on both sides of the boot? If not rotating the highbacks could help too.