Can anyone clarify, but is the factor that was so hotly debated that this additional diffusing element was formed in some part on the tail of the gearbox/rear crash zone, making a mandated safety design/required part have a positive aero effect. I know the aero design presents a complex boundaried volume in which to work and that the rule books are something that is more useful to a weightlifter than an engineer. I have not dug up any pics of 'with' and 'without' diffusers.
We have seen though, that a number of elements in a space can be more effective than just one bigger one, if this could be a factor, but to a limit only. (like multi-elemented front wings as we are seeing developed again)
I am an engineer, not a conceptualist