I just looked at the one I have press-fit together for experimentation. First, I will say that pictures online often distort things for me. Perfect example is recessed panel lines. I can't think of how many reviews have made them look overdone, but when I get the kit they are exactly what I want. Having said that, my gap might be the same as yours. And to me, mine looks out of scale by a bit, but not so much that it ever bothered me. When I first saw that kit, I almost felt like Bandai was putting the modeling world on notice that there is, in fact, a bit of a gap there as every previous kit had no gap. It was like the size of the gap was meant to emphasize the point.
Anyway, about minimizing it. If yours is "correct" but it's a bit to big to live with, you have to realize that there are lots of side panels and other parts that are sized for what the kit has. It may be all those other parts that are also holding it up. If you can get the mandibles apart, my method would be to put some kind of spacer to make the mandibles a little taller. This might/should also create a gap or something around the edges, but it's an area where it might be filled with smalll strips of styrene--thinking of those tiny square pieces that Plastruct has/had. Anyway, something like that stuck into gaps along the edged of the mandibles, I could live with.
Mike Todd