One of the problems trying to set the truck in terms of the stability triangle is that the normal arrangements don't apply. I tried it with two triangles, the joint apexes being on the pivot king pin. I am not sufficiently adept at force diagrams and complicated geometry, so I failed. This is what the late George Coates spent one Christmas doing, to the angst of his wife and family.
The instructor who carried out my conversion course, some years ago, claimed that he could only train on a Flexi, not on a Bendi, because they were different, until I explained that the only significant difference lay in which axle provided drive.
In the end, I completed the course using both types of truck, in two different locations over two days as one had gone unserviceable.