You may also find this section from our Getting Started guide at https://www.8020endurance.com/getting-started-with-80-20-training/ helpful:
Q: My pace (or power) and heart rate zones don’t line up. For example, when I’m in Zone 2 for pace I’m in Zone X for heart rate.
A: This issue is usually resolved by ensuring that you use one field test to capture the threshold of multiple intensity types as outlined in the documents Intensity Guidelines for Running or Intensity Guidelines for Triathlon. By measuring Pace, Power, and/or HR in a single test, the three intensity types may align. However, due to the inconsistent nature of heart rate, it is normal for a given output to result in a different heart rate on a subsequent day. This is a normal phenomenon when using heart rate.