That's what I've been doing and currently am working on.
One thing most EVN lack is character development. One reason may be that most EVN are short stories, often ranging from 5 to 30 minutes, in which there is hardly time to develop a character. However, a more prominent reason may simply be that most EVN writers don't know HOW to develop characters.
It's a bit confusing, I think, but let me explain it like this: when you have a character concept, it always makes sense in your head. But developing the character is a matter of getting those thoughts onto paper. The human brain fills in mental gaps of information, and so a developed character in your head may not be a developed character in your story. Sure, you can know everything from their zodiac sign to bust size, but as long as your reader doesn't, then your story has a problem.
The easiest remedy is to have the characters face conflict in the story. Infodumps are awful; please avoid if possible (and it's ALWAYS possible!). Another remedy is second-guessing yourself. "Should the plot go in this direction? Alright, sure -- no wait, what if the opposite happened? Would that be more interesting to see? Yeah, I think it would!"
I'm not doubting that developers have fleshed out their characters. On the contrary; all that I'm saying is most fail to convey it in their writing. Stereotypes can and should serve as nice templates for character personalities (after all, tropes can't be avoided). However, a common pitfall is to keep yourself locked in that stereotype's box of tricks. "How would that character react? ...Well, how would that stereotype react?" That kind of thinking is wrong. Your character has a unique backstory in a unique time and place, and those factors should influence your character's reaction -- not a stereotype!
Of course, I must also remind you that I'm far from an expert in writing. But I've found that this technique helps me write a better story and better characters. Previously, I approached writing from a fanfiction perspective -- each character already had a (stereotypical) personality, and I was confined to write within those boundaries. No, as a writer of original content, those boundaries are yours to set. Please don't waste that power by assuming you have no control -- the truth is just the opposite.