From Row Size Area you can customize the size of the total combined width of the row header columns for matrix grids. Row Area Size is accessed from the Settings tab of the Matrix Grid view of the Formatting panel.
Set the Row Area Size
The Row Area Size drop-down is located on the Settings Tab of the Matrix Grid view of the Formatting panel. From the Row Area Size drop down, select either Maximum Size or Fixed Size.
Maximum Size (Percentage)
Define the maximum total combined row width, relative to the size of the canvas. For example, if Relative is set to 80%, then the rows cannot take up more than 80% of the canvas. If the given maximum is surpassed, then a scroll bar is added to the bottom of the grid (blue arrow below), enabling users to scroll across to view all the rows.
Fixed Size (Pixels)
Set the maximum total combined row width by pixel; if Fixed is set to 100 pixels, then the combined row width cannot be greater than 100 pixels. If this maximum is surpassed, a scroll bar is added to the bottom of the grid.
Grid Size Settings Dialog
The Row Area Size can also be edited from the Grid Size Settings dialog, which can be opened from the Column Sizing drop-down. From the Grid Size Settings dialog you can customize the Row Area Size and Column Size: