I seem to remember reading that the rear should be two of something higher than the front but I can't recall what. CM's or inch's?
Where do you take these measurements and is it set with or without driver in the car?
Cheers.

As far as I understand it's normally about 1", so 2.5cm higher at the rear. At least that seems to be the recommendation.

What you're refering to is "rake". An inch higher at the back than the front is common although it varies from car to car. Ideallyit's set with you in the car.

This is also my understanding, but I don't see why. You could just as easily keep the chassis level, move the rear suspension pickup points an inch higher, and get the same result in terms of suspension geometry, surely?

Or is it more about aero?

Yes rake. So measured from the front to the rear of the chassis, yes? I have it at an inch. If nothing else, with jk seats, it allows me to see over the bonnet and gets it off the bump stops
I thought I had read in the past about 2 inches though?

Only reason I can see for having rake is to maintain some level of nose-down at high speeds. Otherwise can't think of a sane reason. Anyone correct me?

It feels a lot more balanced and doesn't want to change ends quite so quickly with the one inch. I think it's Caterhams that have two inch.

Aerodynamics

Mine was setup by mnr with 10mm higher at the back, since I changed to 13"s the front has sunk down a bit further.. its a bonus at mot time as its too low for his ramp

It's generally employed to aid chassis balance and weight transfer.