I tried the unit ingame, and it's really rather extreme on this one - even rotating the map to a different angle does not always help. The model and the .nif do look very clean however, there are no obvious problems with it.
And no, there is no hit-box of any kind - the engine derives this behavior from some unknown calculations (possible the scaling or movement limits from some animations auxillary objects, but even if so, i have no idea how to fix it, without screwing that animations). I'm afraid, unless someone else have any idea, or maybe Matt happens to look in here, you might be out of luck with this one.