Shimano has made a lot of money saying that this lever must be paired with that caliper. In reality the issues are about modulation, leverage (what most call power although it's really removing energy) and the feel of the lever under application. Since all this is fed through humans and we have vast differences in hand size, strength, skills and such there's a lot of variation of perceived "working".

I do agree with rccardr in that avoiding the earliest levers with the latest calipers is a good suggestion as that combo is pairing at the extremes of the above factors. Andy