How is soil moisture increase in flex daily calculated?

Hi folks,
I am having trouble understanding how Rachio calculates the soil moisture irrigation displayed in the “more details” for “soil moisture” and assumingly used to calculate how often a zone is watered in flex mode.
For example I created a custom fixed spray head and set it to “nozzle cm/hr = 4 cm”.
My watering for that zone was run this morning for 15 mins, so Rachio should have calculated an increase of 1cm in irrigation, but instead calculated 1.5cm - attaching photos…
What am I missing, or is this a bug?

This is related to my recent inquiry…

That being said something doesn’t seem right to me, since running that zone for 15 minutes should produce less than 1 cm, due to efficiency setting. Are you sure there weren’t any other irrigation events other than that? If you click on the arrow on the left of the word irrigation on your soil moisture chart, it should expand and show if there were any other irrigation events other than the flex. It just seems like it ran for 25 minutes total not 15.