I can't rise my HR above 92%HRm

Hi, recently I've started more training on a road bike with HR and power meter.
But I have always a problem to reach high HR, maximum i reach on a bike (road or mtb) is about 91-92%HRm.
You may ask how i know my max, I reached it on few occasions while running or on my road bike - but on a trainer (204bpm).
(FTP 273W - 3.8W/kg - from 20 mins test)
Outside I can reach >90%HRm in 2 mins, but it has to be near-maximum effort - 158%FTP avg from these 2mins (it's my current 2mins max. -431W)
or I can reach >90 on longer sustained effort, like 10 mins in Threshold power.
Last month I was doing VO2max intervals (in PZ5 - 105-120%FTP), but now I realised that maybe I wasn't pushing myself hard enough,
coz I wasn't reaching >90%HRm. I can 'easily' reach 85%, but later it starts to be real difficult, I mean, my legs will die first.
Is it normal? (I know that everyone is a bit different)
Or should I try a bit harder? (next time I'll try hard-start intervals, to be closer to 90%, maybe at the expense of overall duration).
but definitely, more than 92%HRm just doesn't look like possible.
ah, another thing, I ride flats now
(it could affect things a bit? but my HRm on a trainer I did on flats too, but final sprint had candence probably way above 100rpm, but i don't have any data from it)
my cadence above 105%FTP is 90-100rpm.
But I have always a problem to reach high HR, maximum i reach on a bike (road or mtb) is about 91-92%HRm.
You may ask how i know my max, I reached it on few occasions while running or on my road bike - but on a trainer (204bpm).
(FTP 273W - 3.8W/kg - from 20 mins test)
Outside I can reach >90%HRm in 2 mins, but it has to be near-maximum effort - 158%FTP avg from these 2mins (it's my current 2mins max. -431W)
or I can reach >90 on longer sustained effort, like 10 mins in Threshold power.
Last month I was doing VO2max intervals (in PZ5 - 105-120%FTP), but now I realised that maybe I wasn't pushing myself hard enough,
coz I wasn't reaching >90%HRm. I can 'easily' reach 85%, but later it starts to be real difficult, I mean, my legs will die first.
Is it normal? (I know that everyone is a bit different)
Or should I try a bit harder? (next time I'll try hard-start intervals, to be closer to 90%, maybe at the expense of overall duration).
but definitely, more than 92%HRm just doesn't look like possible.
ah, another thing, I ride flats now

my cadence above 105%FTP is 90-100rpm.
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If you're on the road, just use the highest HR number you have seen and set that as your max.
But, if you have a power meter, then your HR is kind of irrelevant anyway.
You will only reach it if you are in the right condition. Any fatigue and it is unlikely you would get there.
Why do you care what your max HR is?
As above, it doesn't really matter if you have power.
This.
Sad, but true.
I am not sure. You have no chance.
I am not sure. You have no chance.
Sad? Not really, it’s an inevitability of life
Embrace it and live the life you have
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
Here's what you could have had in your youth.
I am not sure. You have no chance.
Also bear in mind the equipment you have to measure your HR might not be that accurate. Are you using the same piece of equipment to measure your HR when on the bike/on the trainer/on a run?