How is 'in AFib' percentage calculated in Apple Watch ECG when resting HR is below 50bpm?

As a fit cyclist my resting HR Can be below 50bpm for more than 12 hours per day. I know on demand ECG is not considered for AF when RHR is below 50bpm. I want to know if ‘in AFib’ 25% of the time is per 24 hours or for times when over 50bpm. It makes a lot of difference!

[Re-Titled by Moderator]

Original Title: Percentage in AF summary - us it per 24hr or only when 50+ bpm?