I don't believe you can. Once you create a custom unlock, you cannot fly outside of it, once inside of it. The rest of the world outside the custom unlock becomes an NFZ. That's why custom unlocks should be avoided wherever possible.
However...
From a Drone savy member of the forum named GadgetGuy from an post long ago.......This just may be whats happening
""You have to be inside the unlock when you launch, because the area outside the unlock automatically becomes an NFZ. If you...