Well, I am by no means an expert on this stuff.
But, here's how I figure my MHR: when I'm doing maximum effort intervals on a hot day, whatever peak I hit. It's typically on my fourth or fifth repeat, when I'm fully warmed up but not too fatigued to hit maximum. Ambient temperature matters - I'll always peak higher when it's hot out.
The old Garmins didn't figure zones from resting. I understand why they abandoned the auto-calculation feature, but for me it really tracked well with how I felt. Zone 1 went from just easy moving around (for me, around 82 bpm) all the way to Zone 2 starting when I hit a slight aerobic effort (for me, around 140 bpm). After that it calculated zones in equal increments to max. Those were useful to me in structuring workouts because I could try to get down to Zone 1 during a recovery interval, which would be impossible if Zone 1 were calculated in equal increments from resting to max.
Now, I'm not at all familiar with Sally what's-her-name's HR workout. It's popular these days. Maybe that would be a better place for you to start...
"I felt [the women's Olympic marathon] was as important as women having the right to vote, because talent, strength, and capability cannot be fully realized if there are no personal rights to allow them to be visible or be deemed significant in the first place." - Kathrine Switzer, Marathon Woman