To achieve your requirement you can modify the ControlTemplate of the ManipulationAdorner element. The Editing Control Templates
article shows how to get and change the default templates of the UI for WPF controls.
In this particular case you can find the Path element with x:Name=RotationPart from the template and set its Width and Height properties. I attached a project demonstrating this approach. Note that the project uses the VisualStudio2013
theme with its Dark variation and NoXaml
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