^ This.
But as I've said before, the text of the rule is unclear in its interpretation.
3.5.1 [snip]
"On all sides, all drivers’ helmeted heads must be at least two inches inside the area enclosed by the cage."
[snip]
First: the cage defines a VOLUME, not an AREA.
Second: the volume enclosed by the cage - and here's where I agree with Mr. Yuck, the "(whatever it is)" enclosed by the cage ACTUALLY DOES MEAN INSIDE the cage.
Though, as interpreted for so long, it's the exterior dimensions the rule contemplates, not the interior.
I have suggested changing the words to something like:
" 2" below the volume defined by the exterior dimensions of the cage (meaning the outside surface of the cage) " .
(I had posted a more succinct sentence, but can't remember it right now - though it's in my posting history).
That's a little more clear than just referencing "the broomstick rule"; where a stick is laid on the top of the cage, and the helmet can't come within 2" of the stick.
(There's got to be a better way to check, especially when the cage is installed close to the inside surface of the car; but that's not my area of responsibility - or expertise ).