Hi Dov,
Thanks for contacting Syncfusion Support.
In Ribbon, If we change the height of TabPanelItem, it will affect the UI of other items like RibbonTab, BackStageButton. But we can increase the size of the Ribbon by using "EnableTouch" property. This property will enlarge the Ribbon control and its items, which would be easy to access in touch environment. We have created a sample by enabling this property. Please download it from the below link
Sample:
RibbonTesting Regards,
Rajkumar G