Task/Milestone order/position on a project

I'm working on an integration where I'm basically pulling task & milestone data out of Clarizen via the api and recreating the same workplan structure elsewhere.   

I haven't been able to determine where the task ordinal or position is stored.  I assumed the position of the task would be stored in a field but if it is I can't find it.   

To test, I created a workflow on workitem that fires on created/updated with no criteria (so it always fires).  If I then go into  a project and start repositioning tasks manually by dragging and dropping them the workflow does not fire.  This leads me to believe the position/ordinal isn't stored on the workitem

To be clear if say I have this workplan:

Milestone A

    -  Task G

    -  Task F

    -  Task A

How can i determine via data/api that Task F is in the second position after Task G?