If you have used a 30 and your current configuration works, then wouldn't you try to replicate the exact same clip spacing on the 13? Seems like you would move the clips to the ends of the bottle as much as is possible and then maybe add a little slack?
yeah essentially that's what I was planning to do.
But I can't be the first person in the world to sling a 13 so figured I'd gather some advice here first.