Wouldn't it be more symmetric to subdivide the inner rectangle and then draw the lines on the outside. This way the thirds are all the same size. Otherwise we chop off the outside thirds and not the center one.
Strangely, I've not seen it done on the inside border before. These are guides to go by, mainly, and I personally don't mind a little asymmetry. I will look deeper into how others set their templates out! I'll put this in the livestream today and see if there's a better way to subdivide for the correct border. It would be on the trim border, and not the safe area.
