Thank you for the writing and for the provided screenshot.
The size of the RadRibbonBar control is calculated according to rules which are described in Microsoft Office 2007 UI Design Guidelines. The size of the area containing the groups is determined by the group with the biggest height (but not more than 60 pixels). If you want to set a smaller height of the RibbonBar, you should set the Maximum Size of the groups. Please refer to the attached screenshot.
I hope this helps.
All the best,
the Telerik team
Q1’11 SP1 of RadControls for WinForms is available for download; also available is the Q2'11 Roadmap for Telerik Windows Forms controls.