I need to set up a shipping restriction for L + W + H not over X inches. Is “total
dimension” that?
That's for total, yes. So if you set it for 40 inches you can have any combination
of dimensions less than 40 fit in that shipping method. Since Lego uses standard
sized boxes for their shipments I reuse their boxes and use Max Dimensions instead
and title the shipping method for that box size.