That formula sucks and heart rate is variable on an individual basis. There are people your age & fitness who legit have a max HR of 160. There are people your age & fitness who legit have a max HR of 195. I would call your max HR observation very typical.
You should trust your own training experience a lot more than you should trust that goofy age-based max HR formula.
Don’t know if it helps you, but I think TR has pretty dramatically increased the maximum heart rate I can tolerate for an hour. I track that metric & in a little less than a year with TR it’s gone from 161 to (just two days ago) a new high of 167. On that day I rode for just over 5.5hrs at an avg HR of 161…so just right at what I could tolerate for only 1 hour less than a year ago.