Hi Mark (owe you a phone call),
Yeah, but I've seen gumbies that can even twist out of that. I can lock down several versions of shiho so that it becomes EXTREMELY risky for uke to twist out of. Locking it down isn't the problem. Hurting or risking hurting flexible beginners who don't know no better is the problem. If I lock them too tight, they no come back no more...
A little forth control pin goes a long way to understanding just one of the possibilities to assuming gumby status.
I am not sure what fourth control pin is but rather than doing the lock down like that picture (and there is film I recall where the GI spins out on Ueshiba Sensei in a classic way so I don't think this is all that reliable), I find it much easier when I sense a beginner start spinning out is to stop pivoting myself and move out in a straight line and drop them softly on their butt. It's not hard on them or painful and they drop every time. It's then easier to have a discussion of how vulnerable spinning out leaves them.