I see your point, the blue at the hip is far too large compared to what MMZOCW present. Though, it's still quite hard to truly make out. Maybe try an alternate version with a two piece armor?
I'm gunna wait to refine the mockup, now. There are many conflicting things. Also, I think if we can get a large version of the Big4 and X on the mountain, we can look at his mid section to at least see that.
There's also that pic of Elpizo killing X which clearly shows that X's abdomen is some kind of light blue/gray.
e+ card 135-D001 Farewell, X
That looks like its part of the blast like the slash on his left leg. Man, more conflicting stuff. It looks like he has bare shoulders like Zero in that card as opposed to the sprite and his in-capsule art. The start of his lower leg looks interesting and hard to make out.