You should predefine the template of GridViewRow against MetroTheme and remove the Padding of the Border around the PART_HierarchyChildPresenter. Just modify the default Padding of 6 to the desired value.
You may get the xaml files for all Telerik Themes from the Themes folder of your personal installation.
the Telerik team
Sharpen your .NET Ninja skills
! Attend Q1 webinar week and get a chance to win a license! Book your seat now >>