I have written about this before and I'm glad to see that Deborah Vogel at The Body Series is writing about it again! Specifically:
"This week's question is from a student curious about why she can do a good butterfly and frog position and yet can only stand in a first position of around 90 degrees. It's not an uncommon pattern and a good one for our students to understand. "
I hope you read this! If you are tyring to improve your ballet turnout you need this information!