Max Rivlin"]

Are you referring to how far away you can be from a point to get a tooltip to appear?

Yes. Is there realy no way? Can I make the points a bit larger or something else?

You can try making the line's midpoint anchors a bit larger. Larger icon size should give you a larger area to get a tooltip:

LineAppearance lineApp = new LineAppearance();
lineApp.IconAppearance.Icon = SymbolIcon.Circle;
lineApp.IconAppearance.IconSize = SymbolIconSize.Large;

ultraChart1.LineChart.LineAppearances.Add(lineApp);

Hi,

this solution sound good. But how do I implement it in a composite Chart. I think I have to put it on my Layer. But I can not set by LineAppearance to my ChartLayerAppearance.

Can you provide a code snipped?

Thanks 

There is an extra step for composite chart layers. Layers have their own corresponding appearance classes.

LineAppearance lineApp = new LineAppearance();
lineApp.IconAppearance.Icon = SymbolIcon.Circle;
lineApp.IconAppearance.IconSize = SymbolIconSize.Large;

LineChartAppearance lineLayerAppearance = new LineChartAppearance();
lineLayerAppearance.LineAppearances.Add(lineApp);

ChartLayerAppearance lineLayer = new ChartLayerAppearance();
lineLayer.ChartType = ChartType.LineChart;
lineLayer.ChartTypeAppearance = lineLayerAppearance;

with the larger icon size, there is a larger hit test area for the tooltip. I'm still not entirely sure what you mean by 'sensitivity' of the tooltip, but when I create large icons my I can mouse over a larger area to get the tooltip, because the circles are larger.