I'd say each "level" is a range. A small range, with the upper end of a lower level butting up right against the lower level of the next highest one.
As you said, there's no way to tell within this range who is stronger without a duel, and based on the Companion, that would have to be a duel where things like skill, speed, knowledge etc. would have to be removed from the equation.
But anyway, it seems a one or even two level difference has minimal effects. And we see that reflected in how women a level or two below another in the WT barely show much deference. This is especially strongly visible among the Salidar Six.