Roof tents on a Gen 3 ?

It's the same as the unbraked towing limit. The hand book stipulation is 320 or whatever but it clearly states unless local jurisdiction differs, which the construction and use regulations act clearly does stating that the unbraked towing limit should be half the kerb weight of the vehicle upto a maximum of 750kg. And yet there seems to be this blind adherence to the hand book even though when it comes to the braked towing limit it says 440 again unless local jurisdiction differs and then suddenly people are only too happy to go with the type approved 1300. Either the hand book is right or the regulations are?