Based on my understanding you could arrange your view's position using the
ViewSortHint attribute. This attribute allows a view to declare a
Hint property which defines how the view should be ordered in the region.
Note that by default when displaying views, the Region class uses a default view sorting routine that uses the hint to order the views.
You'll find more information regarding that in the Prism documentation, Chapter 7:
Also if you want to change how views are ordered the documentation explains that:
"...the Region class provides a SortComparison property that you can set with your own Comparison<object> delegate method. It is important to note that the ordering of the region's Views and ActiveViews properties are reflected in the UI because
adapters such as the ItemsControlRegionAdapter bind directly to these properties. A custom region adapter could implement its own sorting and filter that will override how the region orders views."
I hope you find this useful.