Wolfy - very well put - I have a spreadsheet somewhere ( when I find it again and not one that I authored) that allows easy calculations of what you have explained so well -- thanks and cheers - travel safe.If anyone is wondering what Meggsy and I are going on about, here's some numbers for the CR that might help explain.
Wheelbase is 2899mm (210 TDi)
From the towing a trailer section of the owners manual, the spec position for the towball, which I assume is achieved by the factory/Westphalia option, is 1119mm behind the rear axle. That's the overhang, and the ratio is 0.386 of wheelbase.
Load on the towball is like a seesaw where the pivot is between the axles and any weight on the towball magnifies the weight on the rear axle by ball weight times (1+ the overhang ratio) due to the longer lever arm the towball position has, and reduces the weight on the front axle by the ball weight times overhang ratio.
So for a CR with a ball weight of 100kg, vehicle mass increases by 100kg, rear axle load increases by 138.6kg and front axle load reduces by 38.6kg. At the limit in the MY21 towing supplement of 240kg, it's 332.64kg extra on the rear axle and 92.64kg less on the front.
For Meggsy's extra long tray Navara, assuming 3100mm wheelbase and 2000mm overhang, the ratio is scary at 0.645 so the same 240kg ball weight would be putting some 394kg extra on the rear axle.
As an aside not relevant to air suspension Touaregs just the extra weight and overhang of a WDH makes things worse before they help. Using the Touareg overhang ratio and 240kg ball weight, a 10kg WDH that moves the ball just 150mm further from the axle adds 10kg to GVM, and near an extra 28kg to the rear axle, before the bars are tensioned. So the WDH has to transfer 28kg off the rear axle just to not make load distribution worse! And the longer overhang caused by the WDH increases the yawing (swaying) leverage the trailer has on the tug. Not surprising the manual says no WDH.
Found the link - its American and in pounds and inches I think Extended Hitch Calc (visualsc.com)