Pup wrote:The regs say the major axis has to be within 5° of the reference plain,
Yep.
Pup wrote:which is horizontal.
Nope. The rake of the car tilts the reference plane relative to the ground and adds maybe 2º-4º to the AoA of basically everything on the car: including the suspension elements, "neutral" central front wing section & "neutral" camera pods.
OT:
It's actually a bit odd, semantically, for the suspension to be defined relative to the reference plane in this way: the reference plane exists because otherwise the angle (and thus legality) of parts attached to the sprung part of the car would vary as the fuel load/suspension setup was changed which would be a nightmare to comply with and a nightmare to police. Since the suspension arms are not (by definition) solely attached to the sprung part of the car, defining them in terms of the reference plane reintroduces this problem to some extent.
Back on topic:
The above off-topic excursion makes me think that a sensible team (as McLaren undoubtedly is) will not intentionally create a suspension system which is at peak effectiveness at 5º-to-reference-plane AoA: if you do that you are painting yourself into a corner in terms of setup.