Thank you for contacting the Telerik Support.
In order to resolve your issue, you can set a bigger Width value for the RadHtmlChart. This will give you more space for the chart's elements and the labels should not overlap. Setting this property might look like this:
where you can change the value to the appropriate one.
You can also take advantage of the LabelsAppearance's Margin
property in order to change the position of the series items' labels.
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