The field imposes a nonreal restriction, so within the field (which permeates multiple dimensions) an apparent restriction is placed upon moving objects.

So regardless of the laws a outside the field within the field a sort of light speed net exists that interacts with any object moving [i]apparently[/i] faster than light. The field then feeds the necessary energy to slow the apparent speed of that object to lightspeed, in almost every case this release of energy is large enough to destroy the object.

So if you are shrinking the distance that would prove impossible within the "locked" or "enforced" laws of the field and as the object would move apparently faster than light against the "net".

So the field negates tactical use of FTL within a battle and strategic use around some planets so an attack has to commence outside the field and fight in.