I've done some further research and it may be that the contingency fuel was based on city pair/aeroplane combination statistical method.
an amount of fuel based on a statistical method that ensures an appropriate statistical coverage of the deviation from the planned to the actual trip fuel. This method is used to monitor the fuel consumption on each city pair/aeroplane combination and the operator uses this data for a statistical analysis to calculate contingency fuel for that city pair/aeroplane combination
CAT.OP.MPA.150
I will of course enquire my flight ops department.
AMC1 CAT.OP.MPA.15