So yes, each estimator works great for exactly the opposite cases. But notice that typically, the results of the new formula is much higher than the old one, sometimes by two orders of magnitude (and it shouldn't be difficult to construct examples of much higher differences).
The table also includes the 'average' estimator you propose, but it's rather obvious that the result is always much closer to the new value, simply because
is always much closer to the huge number. We're usually quite happy when the estimates are within the same order of magnitude, so whether it's K or K/2 makes pretty much no difference.
I believe that Mark means geometrical average, i.e. sqrt((small number) * (huge number)).