Ok, now we have more info. It's likely you hang with this group on the flats because you can ride with faster groups on the flats due to drafting even if you're a bit weaker.
Also the formula is worthless as a training tool. One, do a field test, and two base your training off lactate threshold hr, not max hr.
There are multiple threads that elaborate.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.