That is interesting. Zone 2 as 80-90% of LTHR seems strangely high though. For me that would be around 72-81% max HR. I think Coggan has it as 67-85% of LTHR, which works out as 60-75% max HR
Heart Rate Threshold - All Sports: We suggest a threshold increase if your peak 60 minute, or 95% of your Peak 20 Minute, Heart Rate is greater than your currently set threshold.
I use Intervals.icu for my LTHR. It calculated mine at 183bpm after I averaged that for an hour long TT back in September. Interestingly (for me at least) they calculate my max HR to be 199bpm, I think based on Friel zones. I lowered it after my birthday a month back to 198bpm
After you do a effort (IMC the hour long TT) if you’ve improved LTHR it will tell you. You can then manually update your LTHR in the settings. There may be another way @davidtinker may be able to help you out there.