"just a few inches tall."
Admittedly, it took me months indoors to get them past the stage where I could hardly see the plant for all the moss and grass in the tiny pots. And then some of them languished in 1/2 gallon or gallon pots for a whole year.
But once any of them took root in good soil, they exploded up, 5-8 feet tall, then flopped over and kept growing sideways. Once established, they are more manageable in hard, dry clay - a few inches or feet the first year, 5-6 feet the second year, little flopping. They might be happy in well-drained but poor sandy soil - I don't know.
I would try to give them poor soil and very little water. Make 'em work for it, and they might not sprawl so much.
But you may be right, it may be climate. My Zone 8 winter is mild and summers are USUALLY dry and mild. This summer we got a lot of days in the 80s and no few days in the 90s.
Lately I've been cutting them down to a foot or two in late summer, then down to the ground sometime in winter. This fall, I realized they are taking over, so I chopped them right down to the ground after they went to seed and wished I had done so before the seed matured!