I think you are right. According to the formula my max is a measure that I regularly reach when doing longish threshold workouts. I am not sure what my max is, but from what I can understand, few can reach their max HR on a bike (running up stairs might do it, if you have enough stairs) and, once again from what I understand, if you reach your max, you’re more or less ready to puke. I’m too much of a coward to go there.
I’m 67 and have seen 168 on TR workouts (not regularly, but I have seen it) and the formula gives me 155. I see over 160 fairly often, without getting close to puking. I figure 10 beats more over 168 would do the trick.