I think once you get above the standard 60' size the panels don't balance as well due to the wider circle/less arc.
Yes as the diameter increases it creates this stability problem, I realized that when I was setting up the panels. I fiddled around last night, the one place that's really weak is the two gate entrances because the frame around the gate is not very rigid. So I'm going to try pounding posts on each side of the gates and see how much that helps.