Of course, the other aspect about making fuel reserve assumptions is the risk of a systems malfunction.
I heard of one case where a Cherokee pilot went to switch from the left to the right tank (or vice versa, its not important) and the fuel selector sheared off!
Or you could have a fuel line blockage one side etc.
Now its also possible that a passing asteroid could have your tail off
, one shouldn't be silly about factoring things in, but its just another reason why I always felt more comfortable with more, rather than less, fuel on each side.