So as a relatively green cutter (I've probably felled 100 cords of wood), I've always left a little step to force the tree to pivot on that and not kick back or slide off the back of the stump. I cut fast enough that the tree is still standing while I'm pulling my saw out and getting clear (most of the time). When you've got a real leaner, there's no point and I'll do a little relief on the downward side before cutting through from the back - that might not be the right thing to do either.
Do you guys intend to cut a flush stump? Or are you just against leaving so much wood above the hinge?
I've never had a barber chair, but I've had plenty that didn't cooperate.
The tree isn't forced to pivot on the step. It's a safety measure to keep the tree from coming back on you as the face closes and the hinge breaks. Limb-locked trees are a good example of a situation where the tree might be forced back at you on the stump.
The trees decent is controlled by the hinge. Hinge thickness, fiber column height, fiber strength, straightness of the grain, and many other factors decide when and where the tree goes. . . Not to mention the unforeseen factors.
When you step the back like Cody, you're lengthening the fiber column of the hing. Got a corn broom in the house? Grab it and pretend it's you hinge. With your right hand grab it tight (that's your face), with your left hand bend the broom at different heights in relation to the right hand, and observe the fibers (don't break your broom LOL).
So now look at the video of that fir. As the tree began to commit, that tall column of fibers began to bend, at some point they stop bending and start breaking. If the grain is straight enough at the tare, and the forces are great enough, it could continue up the stem and slab or chair -- specifically at the end of his back-cut. An early closing face would make it worse, as the tree would still have a lot of forward energy left.
He could cut trees that way for the next 100, and nothing may happen. . . But it only takes 1 to get ya -- and he's a bit cocky on the "stump lingering" aspect. Once the tree commits, get the heck back, most injuries occur within 8' of the stump.