[Chapter Four]

Tow ball weight affects stability at speed.
In most european countries there are restriction on how fast you can go when towing (80-100kmh), so 5% or less is actually OK and studies have show this.
In the US and most of Australia, you can tow at the speed limit if you choose to.
Studies have show that trailers with a 3% ball weight are stable to 76 km/h, 5% to 110km/h, 10% to 130km/h and 15% to 160Km/h.
There is a big jump between 3% and 5% which is why the Euros opt for 5%. It has shown to be safe for the speed you are allowed to do.
If you are trying to rebalance the ball load, don't put a heap of weight behind the axle, that will make things worse if it does develop sway, even with 5% or more. Put the weight over the axle, but no further. If you can't rebalance safely and get to your specified max ball load, then that van is not for you.
As I've said, I tow a 2T trailer with 110kg on the ball. The car and trailer are loaded so that I am withing the GCM, ATM, GVM and axle limits. I've had the rig over weighbridges to check everything several times.
If you set it up properly you can safely tow 2T with 5% on the ball, just don't expect you can do 110km/h just because the speed limit says you can. (the cars handbook says you can't anyway)