Is that for a solid (dense) cube, or just six even sides to form a box?
Otherwise, seems whoever wrote the description of the force generator bungled the numbers a little.
It's six even sides to form a solid box. The standard description is that a Force generator generates a sheet of Force one inch thick, which can be shaped into....uh...shapes that can be 3D or just other poygons
You have to summon up some of that geometry they taught you to figure out the exact sizes of the shapes, though. I worked out walls, squares, rings, spheres, cubes, a 10x10x5 bin with an open side...Even stairs. And the area of the "disc" shape was about twenty feet across.
I wouldn't say they bungled the numbers. More like, simplified them for ease of use.
Anyway, if you thick about it, a disc three and a half feet across is a pretty big flat area.