Sorry, I meant base depth, not width, and when I said 15-20, I meant
mm, not miniatures.
Check out page 7 again, in the paragraph just above the troop categories/types chart on the left column: "Each unit is represented by a single base (or stand) for mounted and light troops or by two or three bases for other foot units. Essentially this is to permit the easy identification of different types of units, as well as to allow for a more pleasing visual effect."
This allows people to use their DBA/WRG/FoG bases with ADLG, by making stands of units out of 1-3 bases for other systems. Or, as my group has done, you just use the larger bases sizes as single stands, like so: