Your math sounds fine. Basically the lifter is self adjusting anywhere in the range just off zero preload to bottoming out. What I've found is if a lifter is tapping at half a turn, it will tap at a 1/4 turn, 3/4, or a full turn. Only time adding preload to the lifter and having it help is if it is bleeding down too quickly, and most of the time the cause of the noise is something else.
Just start the contact of the screw prior to where you want to end up and you can be right on the 1/2 turn or wherever you want. If I want a half turn I'll start the preload with the wrench positioned at 12:00 and have the screw contact the stud at about 4:00 so things are tight at 6:00.
Hydraulic lifters are very forgiving and that's why Comp just says 1/2 turn, and they don't worry about whether you have 1.5 ratio rockers or 1.65 or 1.72.
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Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
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