My experience is exactly the same as song2siren's. Barre first will automatically draw the index finger up the neck and out of place. So far it works best for me to either place the second finger first, OR 3rd and 4th first, NEVER the barre.

But then, my mechanics are probably terrible and I'm looking for a short-cut. So really, I'm also wondering whether it is best practice, or even an unwritten rule that barre first is the thing to go for - and why?

cheers.