Hmm, possibly true. But for the specific use of a 10'x10' solid forcecage, it's moot because instead of passing 5' through it, you can pass 5' diagonally past it and move the same distance by the RAW.
If I have squares:
12
34
Moving from 2-3 is the same distance as 2-4, and is therefore just as close.
If the plane between 2-4 is occupied by a solid wall of force, then it would take 10' of movement to get from 2 to 4 (2-3, 3-4). Thus, 2-3 is the shorter route.
If the plane between 2-4 is blocked by those force bars? I'd say the scout squeezes through and takes no extra damage.
IIRC, objects that only take up a point (the intersection of four squares, like the center of a fireball) or a plane (the side of a square, like the wall of a forcecage) are not considered to be occupying the square. They may block movement into the square, but not occupation of the square.