Hello Greg,
When you add the NDockZone as a child in the root zone using AddChild method the dock zone was added at the end of the Children collection.
For example if the root zone orientation is horizontal the children will be ordered from left to right by their index in the collection.
To put your zone on left side you have to use the other override of AddChild method where you also have to pass also and the index of your zone in the collection:
_manager.RootContainer.RootZone.AddChild(leftZone, 0);
This way the leftZone will be added on the first position in Children collection and it will be placed in the most left (top) position.
Regards,
Angel Chorbadzhiev