The pull request from UR_ makes it adjustable via Preferences...
Or you can just wait a couple of days until it's in the daily build.
Of course only changeable by menu item: Tools->Edit parameters
I think the NaviCube settings should go into their own sub-group underneath the View group.First insert needed parameter "NaviWidgetSize", type: integer at BaseApp->Preferences->View:
Since there are a few more settings we can think about creating one preferences page only for the NaviCube.