It only affects calculating estimated water usage.
http://support.rachio.com/article/383-how-we-calculate-water-usage
The area shouldn’t matter if you know your precipitation in/hr rate. Using a catch cup test is one way to determine it.
Flex schedules have a small adjustment you can make using the water drop on the edit screen. There are a lot more details here if you are curious
http://support.rachio.com/article/385-flex-schedule-tips
We are releasing much simpler schedules very soon, submitting the iOS app today, you can read more here.
Hope this helps.