Window.TabRatio (Excel)

Returns or sets the ratio of the width of the workbook's tab area to the width of the window's horizontal scroll bar (as a number between 0 (zero) and 1; the default value is 0.6).

This property has no effect when DisplayWorkbookTabs is set to False (its value is retained, but it has no effect on the display).

ActiveWindow.TabRatio = 0.5