Desired.jpg
Hi,
Whether the summaries appear on the same line with the description or on a different line is controlled by the GroupBySummaryDisplayStyle on the Override.
Make sure you set this property to SummaryCells and not SummaryCellsAlwaysBelowDescription.
However, even if you set it to SummaryCells, the grid will still put the summaries on a second line if it can't fit the description in before the first summary cell. So the problem here might be that you have a summary applied to the first column and thus there's no room for the groupby row description and the summaries are getting pushed down.