Hi Travis,
Those 20% are more obvious as you are more trained and your aerobic threshold is higher. To someone that is still doing base training, its not in a good physical form, a zone 1 workout should be enough as reference.
In every workout, what you should focus is on the target heart rate, doesn’t matter you walk now or run , the heart will only understand the target rate that he needs to work. Soon , if you comply with the requested heart rate targets, you will go from a fast walk to a run , or a small jogg to a fast run at a heart rate.
Cheers,
Pedro Carvalho