yup. The half idle guidance goes back before video or even internet. Although in some books it says 1/2 crusing vacuum instead. That at least has a some relation to the purpose of enriching AFR as the engine approaching maximum acceleration or load.
The only explanation I've seen for how we ended up with such a misunderstanding of the power valve selection is Tuner's. You're welcome to read it and decide for yourself whether it helps explain it, because
(a) its his opinion based on his experience and observations and other people may have different experiences and observations
(b) its more about how low PV numbers became popular with hot rodders and racers, drag racing in particular, and not directly about the half idle vacuum method of selection.
See Post 57 in Power Valve Selection: The Definitive Answer
