Very true LYKA, but we should note that the beancounters believe that This statement:
The OFP ALTN fuel is always going to be a best guess, based upon planning factors (fuel req, route, altitude and weights).
is in fact not a best guess but an accurate amount.
They believe that the numbers a computer pumps out are actually the minimum fuel required, and they see their proof in extra fuel not being used.
When I change taxi trip and alternate fuel, none of this is extra fuel. But on the beancounters spreadsheet it shows up like this. A computer OFP is not neccessarily a legal OFP, crap in crap out as always.
The fuel they see as extra might just be the minimum required to make the flight legal. Unused fuel does not equal unneccessary fuel.
In order to protect the travelling public from overzealous beancounters and the harsh reality of fierce competition I can imagine that a margin of 15 minutes could be added to the alternate fuel as a legal requirement.
Painful maybe... But it would be equal to everybody.