Now that you mention it, I recall going through those adjustment procedures in your article when I installed the RM brakes.
Occasionally you have to revisit that procedure. The transmission bands wear at a different rate than the RM brakes so it gets out of adjustment over time.
This article said that when hand brake is in neutral, you should be able to move the car via low and reverse.
I have adjusted my hand brake according to service manual, but in middle position, neutral is achieved, but E-Brakes are firm and holding the car. To move the car, the hand brake comes out of neutral, slightly forward, and low or reverse moves car, no problem.
As I read this article, seems I need to adjust mine so that it’s really in neutral without brakes applied. I would guess based on the article description the car should roll with car running and in neutral.
Running or not, the car should roll easily with the handbrake in the middle position.