The universal bracing strap is used between any 2 parallel straight joiners. It is not necessary to brace planters that are only 4 panels (square or rectangular) smaller than 47.25" on any side as long as there are no straight joiners used.
Note If the width of your panel exceeds 47.25 inches, then the universal bracing strap will not work as it will not be long enough. You can then either use the universal brace (turnbuckle style) and hook it to the straight joiners. Or, you can use the large anchor post in conjunction with the anchor set parts.