I just think a lot of people are putting too much emphasis on the idea of forming a wall here.
Now admittedly, this is probably because the OP asked the question:
Is a wall only required when the Defending team ask for one?
However to me that is a leading question, based on a false premise.
It implies that a wall is sometimes required.
However that's not the case - there is no requirement (or prohibition) in the laws relating to the forming of a wall.
The referees first job at a free kick within shooting distance is to decide whether to make it ceremonial or not. If you've decided on ceremonial then your job is to ensure that
all opponents are back the required distance. Whether some of those opponents form themselves into a wall or not is completely up to them. It's not the referees concern, at least until or unless it actually happens.
If you've announced that it's on the whistle and they decide to form a wall then yes, managing it becomes part of the whole ceremonial free kick business.
But as far as I'm concerned there's no real need or reason to liaise with them prior to them starting to form a wall. As mentioned before, it's completely up to them. They either form one or they don't. All the referee has to do is to manage things as they present themselves.