In order to change the docked position of a RadPane you will need to:
- Create a new RadSplitContainer and set its InitialPosition
- Create a new PaneGroup and add it to the SplitContainer's Items
- Remove the Pane from its current PaneGroup and add it to the newly created PaneGroup
- Add the newly created SplitContainer to the Docking control's Items.
I created and attached sample project for you with the described approach, hope this is helpful.