I must confess that in my teens and twenties, I loved 'Mansfield Park' rather in spite of Fanny than because of her. Like Fanny's rich, sophisticated cousins, I didn't really get her.
You can get this feeling of the English or Scottish or Irish or Welsh fairy, but it is by nature very elusive. It would be possible to pin down a German fairy, but the English one just vanishes, becomes the shadow under the trees.
I can write most places. I particularly like writing on trains. Being between places is quite liberating, and looking out of the window, watching a procession of landscapes and random-ish objects, is very good for stories.
In some ways, 'Mansfield Park' is 'Pride and Prejudice' turned inside out.
'Pride and Prejudice' is often compared to 'Cinderella,' but Jane Austen's real 'Cinderella' tale is 'Mansfield Park.'
One way of grounding the magic is by putting in lots of stuff about street lamps, carriages, and how difficult it is to get good servants.