1. this has nothing to do with duration, so a new cam may require nothing at all.
2. higher life doesn't always mean a reduced base circle, a non-welded regrind always has a reduced base circle
3. base circle reduction needs more length: 1/2 the reduction
4. more lift needs less length: 1/2 the lift increase
5. final result depends on how the cam is ground and the rocker ratio