Impervious to Monowire?

[jacobmuller]

The following line, from UT pg 163, bewilders me:

Since the monowire is only along a blade’s edge, it cannot cut into a flat surface.

What is "a flat surface"?
Does this mean:
You can cut up anyone in armor but forget trying to go through walls? Ditto AFVs? Chop off their gun barrels, etc but you can't use a monowire blade to slice through the hull (unlike a lightsaber through a blast door).