You can modify unit size via the unit prod 11 file, I suggest you use gnome editor it lays the unit and build prods as long as projectile stats out in a very easy to edit format. You should be able to find it on the Org downloads page under GnomeUnitbuild_Proj_editorV2.0. One thing to note as garrison sizes per castle are limited when making large units you will need to mindful of this...LOS