Here's an additional tip... To get a better sense of the influence area of the Mag Zone, change its display properties to Wireframe. On the PC, you can do this by selecting the Mag Zone and hitting Control-Shift-3. (Dunno what the hotkey is on the Mac.) Or you can select the Mag Zone and use the top menu: Display menu -> Element Style -> Wireframe. You can also change the Mag Zone to a solid display type (facetted or smooth shaded) then make the Mag Zone semi-transparent using the Material room.