Dreamland
You may be correct, but in the example I gave the flight time would have been just short of 13 hours (or 720 minutes) thus, in your book, requiring 72 minutes Contingency Fuel.
So, 1.2 hours at the end of flight fuel burn of say 8 tonnes/hour = 9.6 tonnes contingency [I said 14.4 as 10% of trip fuel and the flight mentioned had 3.6 tonnes], still 6 tonnes more fuel, even using your rules, and thus planning to land with over 2 hours fuel remaining - easy to make fuel decisions when you hide behind rules like that.
(Mutt's tankering from the sandpit into LHR is irrelevant and is doubtless down to cost - even if it does nothing for the environment, and yes, we also tanker to a few destinations for the same reason, but more like 5% of destinations rather than 100%)