Tom, John,
The first time I built cages from CRW I made the diameter 10 squares. That came out to about 19”. I found that WaaaaY to small. By mid season I couldn’t find room inside the cage for any more branches. And I refuse to cut them back. So I was tying vines to the outside of the cage.
Kind of defeats the purpose of a cage me thinks.
I remodeled some into 24 inch diameter and am trying to use the small ones for the smaller plants and the 24” ones on the monsters like Zogola etc.
Don’t short change yourself or your plants.
Just my experience. Your mileage may vary.