If you are doing extra flying hours for any reason (such as minimising nav fees) the extra fuel costs are only a proportion of the total additional costs. There will be extra crew costs (directly proportional to flying hours), maintenance, and other related expenses. Across the fleet you may need to drop one or two rotations, with their associated revenue, in the same way as if your destination is just that bit further away.
The linked article of course patently fails to understand any part of this.