Empire Detachments
 

I'm not sure if this is correct or not, but you can't increase the size of units within a detachment (example; swordsmen being a detachment of Greatswords) or if you can then it's pretty archaic, because neither the prompt for manually specifying the unit count works or manually pressing the + or - buttons.

Not seeing the problem; detachments max out at half the size of the parent unit so you can't increase the basic detachment of 5 unless you first increase the parent unit beyond its minimum size.