Nice vids! I'm guessing from the end of the "Second flight of the FT Mig-3" that the Mig-3 just needs to go fast, to stay airborne in a bank. It seems like you can fudge it, and do slow, level flight, but If you're going to throw a wingtip up, you need airspeed to keep her airborne.
I ran into something similar with my Spit maiden. The launch scared the crap out of me, so I slowed down. As soon as I banked to come around again, she dropped like a rock. I had to quickly increase the airspeed to keep her going. I'm thinking I'm lucky it didn't stall out all together. Though a lot of that may simply be that our Swedish FT friend designed one heck of a wing for the FT Spitfire. He wasn't even concerned about the degree of the dihedral. He was all like "Meh. So long as you got some."