Hi Ralf,
Thank you for your interest in Essential XlsIO.
You can change the width of the chart by setting the property IChartShape.RightColumn.
[C#]
//Embedded chart position.
chart.RightColumn = 25;
http://websamples.syncfusion.com/samples/XlsIO.Windows/F64376/main.htmPlease let me know if you have any other questions.
Thanks,
Melba