To reproduce:
- Create a dpi aware application and add a checkbox to it. 
- Change your DPI setting to 200% and start the application.
- The checkmark is not scaled only the text is. 

Workaround:
this.radCheckBox2.ButtonElement.CheckMarkPrimitive.CheckElement.UseFixedCheckSize = false;
this.radCheckBox2.ButtonElement.CheckMarkPrimitive.CheckElement.MinSize = new Size(100, 100);