Building a monoclinic single lattice structure

Dear LAMMPS users,

I want to build one monoclinic lattice structure in the LAMMPS. So I have everything, including a, b, c, Gamma, and all 14 fractional positions of basis atoms. So during building the single lattice every things look good. But, when I get to the step of defining the prismatic region something is not clear for me. In the command " region Ali prism 0 xhi 0 yhi 0 zhi xy 0 0 units box " how should I chose xhi yhi and zhi to have a full correct periodicity and build a single correct lattice structure with 14 atoms. In other word, is there a specific relation between simulation box size and my lattice structure dimensions?