Theory works with small numbers too... Take 2, 4 and 7.

Raw distance (smaller value wins):
2 --> 4 = 2 <- closer by distance
7 --> 4 = 3

Ratio (value closer to 1 wins):
2/4=0.5
(7/4)-1=0.75 <- closer by ratio (edit: ok sorry this is bullshit but somehow it works.... xD)

(-1 because the ratio will be represented after the decimal point)

And when it comes to estimations I would say that the ratio/magnitude is more important than the pure numerical distance.
And well... in theory this means that 6 is closer 4 that 2 is, even though they are equally distant from 4. :D