A couple of the larger minis (Another one I've seen is the Guijia) have a two-part chest with half of the arm pegs on each piece, so if they don't slot together absolutely perfectly the pegs don't line up and you can't get the arms on without big gaps. Obviously somebody's managed to put these things together without gaps. How do you do it? Or did you just use greenstuff or something to plug the gaps? I would send a pic of what I mean but I already glued it together and don't want to take it apart unless I know what I'm gonna do to fix it.
Lots of filing and dry fitting before gluing is the usual way to get rid of gaps, using wet paint or ink to work out which bits are touching can help guide where to file.