I've got nothing else to do for now, so I'd like to propose a theory: Square Theory (no, not Square Enix).
Essentially it's a modification of box theory to an extent. We can all see that the portraits on the side are rectangles with a greater height than width (essentially a 2:1 ratio). So here's the idea: what if the portraits were perfect squares? And the side of the square was equivalent to the width of the current boxes? That would mean:
[6 row squares x (6 column squares x 2) ] x 2 sides = 144 characters