I agree about the sizes less than a gallon, they dry out too fast for me, an even width and height seems to work best for me as well, wider might be a little better for growth but takes more watering. I’ve been messing around with 80% compost 20% biochar, great results for up to 3 gallon containers last year, moved some of them up to 10s with the same mix to see how they do. Those look nice, thanks for the tip.
Biocharred all the dead fig tops today, got maybe half a yard from a pile the size of a minivan! It looks like nice stuff.