It’s a matter of proportions. To avoid that gap the whole nose should be cylindrical in fighter mode which is certainly not according to the line art, where it’s fairly obvious that the front section is wider than the rear one, making it impossible to fit it in the chest plate.
Besides, most of the good previous renditions of the YF/VF-19 –and I’m not including the Hi-metal- had that gap and I don’t remember anybody complaining about that.
See these:
Thanks actar.files.wordpress.com for the pic