I’m gonna give you some bro science right now. So take it with a grain of salt.
I am in the same boat in terms of where I sit in my periodization: aerobic base building. My main goal for September and October is to accumulate as much power z2 as I can.
However… I often blend in some Power z3 tempo into the mix and thus my HR ticks up a bit more into HR z3. I’m comfortable doing a lot of that type of training (high z2 / low z3) and find that I derive a lot of training adaptations from consistently hitting they zone. This isn’t just my opinion either. I’ve heard a lot of other endurance coaches talking about prescribing a lot of work in that zone because it is almost purely aerobic.
One thing I’ve done this week to change it up was to go out and maintain a low cadence (65rpm or so) to tax more of muscular endurance. This keeps the HR low and the torque high (which benefits strength, biomechanics, pedaling efficiency, etc.)
Lastly (and somewhat unrelated, but I think it’s important), as scientific as training is, there is no body of research that will tell you how you’re feeling. I’m not a proponent of Whoop and other feedback devices. We ought to be able to know our OWN bodies. This season, I’ve learned to listen to my body. To the point where I’ve literally gotten up early to ride, felt like total crap, and decided to go back to bed (as extra rest was the better use of my time). If you’re feeling good, and your HR is just a little higher than you’d expect, don’t sweat it. But if there are other factors (HR is way high OR way low, you feel like crap or just tired), dial it back.