Its all Black Magic.
My 2000 Petrol has a Hayman Reece Bar, 3300kg max GTM, 120kg ball weight stamped on the plate.
When you read the manual
2.5 Deisel GTW 1400kg Max vertical load 210kg
4.0 Petrol 2268kg 340kg
When you read the manual fine print:
"The tongue weight for the 4.0.gasoline engine (maximum vertical load at the trailer coupling point) must not be less than 226kg but cannot exceed 340kg"
"For the 2.5 deisel the toungue weight(maximum vertical load at the trailer coupling point) must not be less than 140kg but cannot exceed 210 kg."
Go figure......... I use the 2268 GTM and then keep my ball weight reasonable - usually 120-140kg.