Rocker ratio changes duration?

[68Formula]

I believe advertised duration is based on somewhere between 0.004 and 0.006" valve lift depending on camshaft manufacturer. The of course, the 0.050" lift that a lot of people compare. When you increase rocker ratio, the point at which those lifts occur happens sooner, so effectively the duration between those valve points is longer. But I doubt you can calculate it, as you'd need to know the lobes ramp rate at those points. You'd have to physically measure it.