How did you set up your zone 2 on your watch? Sounds like it might be set a bit too low. My Garmin worked out my zones automatically but set my zone 2 off what it thought my max heart rate was during a parkrun. I was able to adjust it higher manually based on 180 minus your age, plus 10 if you have been running for a while and are injury free. I rarely ever push to max nowadays so my garmin just did not know. Lots of my friends have had theirs tested with all the high tech gear but my guess work based of Maffertone seems to work fine for what I need.