Currently ToolTips in RadChart can be shown only relative to the mouse (what is know as PlacementMode.Mouse). The tooltip positioning logic is hard coded and unfortunately it is not possible to change the position of the tooltip.
For our new charting engine we have created a new, more flexible engine that supports different positioning modes and gives you more control over the positioning. Please take a look at this online demo that demonstrates this new engine.
the Telerik team
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