Al, did you all ever check what the spring pressures were at installed height?
With mass produced springs, you see a lot of variance.
It's a painstaking effort we take to match the spring sets, but we feel it's worthwhile since everyone is setting these clutches up based on spring heights.
In a perfect world, we would come up with some sort of scale to measure the pressure it took to move the spring retainer (thinking like a valve spring tester for an assembled small block Chevy head.)
Since we know that we're running these springs in the installed range of ~.200" to .250", we try to aim for that resolution when we match springs using an Intercomp digital spring tester. The consistency of the clutch, wear, and performance is worth the effort in my opinion.