By units reinforced, do you mean the total count of units there can be in a detachment? If so, you can specify that in the SetDetachmentSize function, the MaximumMemberCount parameter.
EDIT: There is also the DEFAULT_SIZE constant, which refers to the same thing, but is applied by default unless the SetDetachmentSize for a particular detachment is called.
I have added a How to use section in the description (including help for GUIers, if you're one).