well it's a pretty dodgy drawing then. their swing arm doesn't use the roll centre in the diagram, it's originating from the centre of the axle, well below the RC!

And I stick by my point that the instant centre (why don't they just call it that?) is alot closer to the spring eye than they illustrate - their illustrated 3/8L is nowhere near to scale.

Even their roll axis term is misleading. In suspension terminology that is normally used to describe the line between fornt and rear RCs. Here they use to describe the axis the rear axle rotates around.

It's like they are trying to confuse/mislead people. At least I guessed correctly they were trying to describe the instant centre... I got something right at least.