Thanks for the compliment jbgibson.
A you pointed out, I am well aware of the unrealistic flows of some of the rivers. But to be frank, I just sticked to Facubaci's drawing.
I can't speak for him, but I think that a "fantasy" world is not necessary realistic. Personnally, I like a lot a comic book with a big river cutting the continent, flowing each side from it's center and suddenly boiling and carrying stones on day each year (a non predictible day).
For me, the most important is coherence. On world has to follow its own set of rules, even if it's fantasy rules defined only by magic.

Facubaci may tell you more.
Thank for you kind concern !