Steve - noseweight isn't a constant, it depends how you load the caravan.
For stability the noseweight should be as heavy as possible BUT must never exceed any of the limits set for the car, the towbar or the caravan.
The Caravan Club adds a recommendation of 7% of caravan's MTPLM but still subject to the above limits, although it's not clear where this figure came from.
If your Passat looks "overloaded" check out the three limits above and test your noseweight, in touring trim, to ensure that you're not exceeding any of those limits.