I use LTHR. Though I haven't done the 20 minute test sample that Joe Friel suggests in over 8 years. In the last couple years, my max HR has started declining from the 180+ bpm that was fairly constant for me during my 50's and early 60's.

Your Karvonen Zone 2 for your HR seems close to what my LTHR zones would be if adjusted for max. Maybe just a tad lower BPM, but not much.

However I can seldom ever ride at zone 2 in my area as it's constant rolling hills. Although for the few times I can ride in a group I have managed to get some time in zone two. But never more than about a third of the time. I don't put much emphasis into z2 at all. Only if I cycled 300 - 400 miles a week or better might I think getting zone 2 benefits as a need.