Hi Karver,
Thank you for your interest in Syncfusion product.
If you want to calculate the summary row value depends on the another summary column value. It can be achieved through some workaround with QueryCellStyleInfo event. Please try using the TableCellIdentity.SummaryColumn and VisibleColumns property in QueryCellStyleInfo event to achieve this behavior. The Summary Column used to placed the calculated value into summary cells.
Refer the sample in below link:
http://files.syncfusion.com/support/samples/Grid.Windows/Forums/GGCSummary/main.htmThis sample demonstrate your requirements with GridGroupingControl summaries.
Let me know if you have any queries.
Regards,
Lingaraj S.