Heart rate from Polar

I have been wondering for a while what the heart rate entry is that's being synced from Polar. It seems to take the entry from a random time of day and at a random level. It's neither an average, nor the lowest or highest of the day, and on some days it doesn't create an entry at all for heart rate. The other stats from Polar (activities and sleep) are working fine for me and are accurate but the heart rate one remains a mystery to me. I would like to suggest to have it sync the lowest heart rate of the day instead of whatever the current metric is, should their API provide that.