[Warbreaker] Strenght of breaths

In the coppermind entry for Heigthening the note at the end states:

The numbers given above are only estimates, as very little is known about the upper Heightenings. Indeed, even for lower levels, achieving a given Heightening may require fewer or more Breaths than is stated above, depending on circumstances and the strength of the Breaths.

That last part is what got me to wonder, are there normal breaths that are stronger than others? Does everyone on Nalthis receive the same amount of Investiture when they are born or are they a little different?