Hindsight is a wonderful thing, I agree though, having defenders on the post is useful but with the amount of free headers we let teams win at corners I'd imagine that's why we don't do it. Jones was obviously under instruction to "retreat" to the near post if the ball went over him as he does that but nobody does it at the back post. Crossley seems to be in charge of setting us up at set pieces so maybe he see's it from the goalkeepers perspective and they don't like having defenders on the line? Who knows.