@jemanner, when do you plan on starting up your watering schedule for spring?
As Franz mentioned, Flex schedules will calculate the soil moisture reservoir on a zone by zone basis using the zone attributes selected. Think of this like a water gas tank -- the first watering has to fill this gas tank, then it will refill at the MAD (managed allowed depletion) threshold set for each zone. We default to 50%.
If in doubt, it's usually best to test Flex on one or two zones first, then roll out to other zones after you're comfortable with the settings and watering times.
Hope this helps. Thanks for your support!