How to set the right HR Zones for Fenix 6?

Apologies if this isn't the right forum for this.

One of the things I really want to credit Garmin and my new Fenix 6X with is getting me to pay a lot more attention to my regular fitness routine.  I've always just gone out and run, but now I'm a lot more engaged with the numbers, which may or may not be a good thing (but that's a topic for a different thread).

When I got the watch, I just used the default numbers for heart rate, whatever those were. I assumed the watch would measure my workouts and figure out the right max heart rate and zones for me. And maybe it does? But if it helps to get more accurate reports and recommendations, I'd like to know if I should manually set these instead?

Just looking at my numbers, it seems like the majority of my runs are squarely in Zone 5. Which seems like a bit of a stretch to me. I tend to push myself with every run, but I'm not all out sprinting, it's a sustained effort throughout a 4 mile run. It makes me think Zone 5 should be higher, and I should be calibrating Zone 4 to reach into the 160s? 

Anyways, are there any good resources I should use to get the zones right, preferably ones that refer to how Garmin breaks down the zones?

Btw, I left the "temperature" numbers in because, hey, it's the topic of the day. Ain't nothing like recording a 13 degree during a run, right? :)