It's been a while since I've bothered to use it/all the Big Blue's features, and I can't quite picture where that bit is atm (you got a better pic?? One showing all if the arms/components that match up to the Spyder maybe??
I'm not in a position/able to dig BB out atm, he's under too much stuff that's been used more recently! Kids, why can't they put things back where they came from!! And who was it who said "They'll get better once they've turned 20... then 30... then 40; only now they're all over 40, and they
STILL aren't any better at that!

But...
Doesn't that hinged bit flip up so that as you slit the jack underneath and then raise it, that bit inserts up into the gap on the other (or front?) side (end?) of the spar, helping hold the whole thing secure and stopping it slipping off BB??
Like I said, it's been a while, and my forgettory does sometimes work overtime on details like that (but my muscle memory is good, I can still run the forms with or without a sparring partner,
and drive the Test Track at the Bend blindfolded without missing a corner or hitting a kerb, a bump, or a guard rail!

)