I find that very helpful. I think the obvious dividing line may be with the whip. I can certainly see that as being a parliamentary function. But the House leader and deputy leader I see more in terms of party office, even though they do have duties in the House.
What we're trying to achieve here is to address the position of the person as being something different from a member of Parliament, in addition to a member of Parliament. But I do take the point that the whip is pretty exclusively within parliamentary roles.
If I could suggest a friendly amendment to myself, I would remove the reference to whip.