Our ToolTipInfo struct, which the grid uses to display the cell tooltips, exposes a 'MaxWidth' property, which allows you to restrict the width, but not force it any bigger. You could use this mechanism to prevent the tooltip width from getting any larger than the width of the column, but you would not be able to force it to that with when there is not enough text in the tooltip.

There is no publicly exposed property or event that gives you access to this struct, but I think you might be able to work around that. The UIElement class exposes a settable property, ToolTipItem, which is of type Infragistics.Win.IToolTipItem, so you could use the IUIElementCreationFilter interface (handle the AfterCreateChildElements method) to intercept the initialization of these elements, and then set the ToolTipItem property of the CellUIElements to a class that implements the IToolTipItem interface. That interface only exposes one method, GetToolTipInfo, which passes you a reference to the CellUIElement, and a ToolTipInfo struct.

You may have arrived at the conclusion by now that this is too much work for the requirement, so you might alternatively want to submit a feature request for a property that allows you to control this.