The following article described the adaptive behavior of the RadNavigation control
The button could be displayed at the leftmost or rightmost side of the RadNavigation control. This feature could be managed by the MenuButtonPosition property, which accepts two values : Left and Right.
To force your content to appear at a maximum width of the device within the browser viewport and prevent horizontal scrolling on a full-screen browser, add the meta-viewport tag to the header of your pages:
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
In the figures below, you can observe how the layout of the RadNavigation changes, regarding the size of the browser. In Figure 1, there is enough space to display some nodes in the RadNavigation and some under the sandwich-like button,while in Figure 2 all nodes are paced under the button.