Legs give out before max HR

It is completely individual….trying to tell you what is “normal” is a guess.

But your overall training plan is pretty much just a guess, too….you are training by “feel” and then using a variable metric to help gauge those efforts.

There’s a lot on HR in Friel’s book. Also, books written in the 80s and 90s on HR training.

Knowing your steady state threshold HR would probably help you anchor sweet spot. Above threshold, just go max repeatable effort.

This is very individual and you cannot really generalize. I’d just observe and look for relative changes, e. g. if your heart rate at a given effort and level of fatigue is unusually high or low. Heart rate recovery during rest intervals is another one.

Your quoted values seem reasonable, though. When I am well-trained, my threshold heart rate is also in the low 160s (158–165 bpm, I’d say). VO2max workouts and ramp tests can push it to the mid-170s. My max heart rate is about 185 bpm, so lower than yours.

Yes and no. It’s more, I am setting my training based on what I think they should feel like, and using HR and power to modulate effort mid-interval. Rather than using a test to set training power and taking that as gospel. I THINK I have gotten much closer to hitting the mark this way than through trusting a test.

I’ve noticed this is more common with indoor rides, when the warmup is short and my heart rate is still low (especially prominent with short intervals) ie total time at prescribed power range = 100% but respective time at HR Zone barely leaves Aerobic let alone threshold

Speaking of threshold HR. When you do a threshold interval, your HR usually stabilizes around a certain level. Mine is the high 160s. If the OP is exceeding that HR comfortably in VO2max intervals, then as a first approximation that’s a good thing.