Figured bass is automatically organized into rows according to the number of rows required in each system independently. By default, rows are aligned at the top when below the staff and at the bottom when above the staff to minimize the gap between figured bass and the staff.
The vertical position of figured bass is determined by the staves above which they are set to appear and your per-layout setting for their staff-relative placement.
You can move individual figured bass figures to different rhythmic positions in Write mode. They are positioned by default according to your settings in Engraving Options. This includes Dorico Pro’s kerning, which applies across whole systems to ensure all figures and alterations are legible.
You can move figures and hold lines graphically in Engrave mode, but this does not change the rhythmic positions to which they apply.
You can change the default positions of all figures project-wide, and set values for the minimum gaps between rows of figures, figures and the staff, and figures and other items, on the Figured Bass page in Engraving Options.