BUT WAIT! THERE'S MORE!
Let's really confuse the OP.
There's the philosophical debate on setting lifter preload. Let's take a theoretical lifter that has plunger travel of 0.200. ACTUAL plunger travel of YOUR lifters may be different--anywhere from single-digit thousandths (.008, as an example) to more than a quarter-inch.
Point is, SOME guys want very little preload, .025 or maybe less, so the lifter can't "pump up" at high RPM and keep the valve open. With the plunger near the top of it's travel, there's very little compensation for wear at the cam lobe, lifter bottom, or rocker arm.
SOME guys want the lifter plunger somewhere in the middle of it's travel, around .100, which is what the OEMs tend to suggest. If the valve seat or valve face--or both--wear, the plunger has room to adjust lower in the lifter to make-up for the wear. If pretty-much anything else in the valvetrain wears, the plunger in the lifter has room to adjust higher in the lifter to compensate for that wear.
A FEW guys want the lifter plunger nearly bottomed-out, somewhere around .175 or deeper, so the plunger can't bleed-down and reduce valve opening when used with stiff valve springs. With the lifter nearly collapsed, there's very little compensation for wear at the valve seat/valve face.
Which is why the reduced-plunger-travel lifters became popular with hot-roddy and high-horsepower types. With only a few thousandths of plunger travel, the plunger is simultaneously near the top of it's travel, AND near the bottom of it's travel, allowing almost no pump-up, and not allowing plunger collapse when used with stiff valve springs to alter the valve adjustment much. Problem is, there's almost no compensation for valvetrain wear.
On a stock- or mostly-stock engine, in normal service, I'd want whatever the factory spec for preload is--assuming the lifters have stock amount of lifter-plunger travel. I wouldn't be buying the severely-restricted-travel lifters.
@Schurkey, this is as simple as I've ever seen it described.
Yup. It don't get any easier that that.
I'm trying to wrap my head around (a) why this method works and (b) why I've never seen it written down.
Is there an unstated assumption / requirement / fact, here, that at least half the valves are on the base circle of the cam, regardless of camshaft orientation?
Yes. At least half the lifters are on the base circle no matter what position the cam is in. Any camshaft that has less than 360 degrees of advertised duration-plus-clearance ramps will suit this procedure. So perhaps a maximum of 320 degrees of advertised duration, with 20 degrees of clearance ramps on the intake and exhaust lobes.
Put another way, virtually all hydraulic cams have 360+ degrees of base-circle. Remember, a full turn of the cam is 720 degrees.
For the record, I shamelessly stole this method from a guy with username "
Motordaddy" on another forum.