Well i don’t believe that Fairytale land is under Storybrooke.
I wasn’t sure about this either but I just re-watched the What Happened to Frederick episode and now I’m pretty sure that FTL is under Storybrooke because when AWB is telling Emma about the water from the well he tells her that the water comes from a spring from a lake under the town of Storybrooke that will return to you something you have lost. This is obviously in reference to the magical lake that frees Frederick from his curse, so the lake is under Storybrooke.