I don't know anything about aftermarket skis or hulls in general, but my guess is that the box is not placed there to frame the E-box.
My guess is that it is there to function as a rib to add extra strength to the bulkhead wall behind it.
My guess is that problems with the bulkhead not being strong enough for whatever reason, front foothold, landing nose first, etc. were not discovered until the first skis were popped out of the production mold.
That is why the work looks sloppy. Because it was added later, rather than designed into the original mold.
But one thing is friggin' sure. I have no idea what I am talking about. I have no experience to base my speculation on. And I shouldn't be posting in this thread.
If it is clear that my speculation is wrong, please be direct, even rude, but please tell me.