How to Hide the Minimized Area
To hide the minimize area you can use the MinimizedAreaVisibility property and set its value to Collapsed.
<telerik:RadOutlookBar x:Name="RadOutlookBar1" MinimizedAreaVisibility="Collapsed">
<telerik:RadOutlookBarItem Header="Item 1">
<TextBlock Text="Item 1 Content" />
</telerik:RadOutlookBarItem>
<telerik:RadOutlookBarItem Header="Item 2">
<TextBlock Text="Item 2 Content" />
</telerik:RadOutlookBarItem>
<telerik:RadOutlookBarItem Header="Item 3">
<TextBlock Text="Item 3 Content" />
</telerik:RadOutlookBarItem>
</telerik:RadOutlookBar>