Hello, I think that you use photoshop for check it, with a downloaded box. I do not have near any japanese famicom box, but measures for
Super Famicom box are:
19cm
10,5 (10,6)cm
3cm
maybe you see contradictions because measures are not 100% the same, and it depends that how you measure it, sometimes it is
between 18,9-19 cm, and sometimes folded areas do the box not exact in front size or back.
I used photoshop for check Famicom measures for
vertical box are
13,7x9,5x2cm (Akumajou III box)
Horizontal box
13,8x9,5x2cm (Final Fantasy III)
I hope that this have usefull for your work.
Regards.