The difference, or a large part of the difference, between Fantasy and Sci Fi, as far as I can tell, is that Sci-Fi imagines it exists in the real world, while Fantasy imagines it exists in a world besides the real one.
This is why Christian ‘Fantasy’ like Pushing Back and the War of Tour Hote feel like Sci-Fi (and the author will admit that at least War actually is Sci-Fi). When an atheist or agnostic writes about magic, he writes about something he believes doesn’t exist, so it feels like Fantasy. When C.S. Lewis writes Angels into the Planets Trilogy, and Bruce Burns has wizards casting Demon-empowered spells in War of Tour Hote, they are both writing about something they know to be real. And so, Christian ‘Fantasy’ often feels like Sci-Fi unless the author intentionally makes a completely imaginary world (Narnia, Middle Earth, etcetera).
I do not dislike Sci-Fi. But I have always preferred Fantasy. I love Narnia more than Thulcandra. I hold Thulcandra to be the superior creation in some ways, but the fact that Fish is usually healthier than Steak does not change my preference for Steak.
Just a clarification of a vague idea that has been wandering through my head of late.