In practice, you'd have some friends on your list even when you were down a couple of blocks (at C for the portas, for exmaple) and couldn't actually get throug

In practice, you'd have some friends on your list even when you were down a couple of blocks (at C for the portas, for exmaple) and couldn't actually get through, or it was definitely at the edge of range and you might just have got a signal through if lucky (I tried down there and never did), so there is some lag involved, but some intelligence helps you figure that out.