Most folks doing this use an open face notch 70 to 80 percent of the tree diameter then push or pull the tree to close the notch. Usually done with an ax. No barber chair.
I've never heard of anyone doing this with an axe or an open face notch. Most guys are using 30-50cc saws, but there's a lot of us converting to Silky's because of the lack of weight and speed at which a good handsaw cuts these <4" trees.
You'll never get a 12" tree to "hinge" - just not gonna happen. They barber chair, or simply break off. If you're cutting a big open face notch, you've already removed what should be the holding wood in a habitat "hinge" cut.
So to explain the process to the folks who seem to be experts at something you blatantly profess knowing nothing about...
You "hinge" the tree by cutting about 2/3-3/4 through the back side of the hinge, and LEAVE the cambium layer on the opposite side of where you just cut to allow the top of the tree to continue to live (typically 1-2 years from when you cut it). You then pull the top of the tree down, bending it at the "hinge" you just made.
The smaller trees respond better than bigger ones. Not many people will suggest attempting a hinge on pole size or larger trees as they just don't work very well. Danger isn't even part of the concern, it's a matter of effectiveness. There's no reason to risk dropping a big tree on you when it won't produce the end result you want anyway. So the larger trees are always traditionally felled, and then the smaller ones are laid down on or around them to fill in the open space.
This is a video sitting in a 1/4 mile long wall of vegetation created with the hinge cutting process:
(click on the pic to play)
I was out squirrel hunting and wasn't even in camo (other than my muck boots) when I stopped to check emails leaning next to a tree and 3 deer showed up.
The forester who did my management plan was disgusted with the project. He saw lots of money he wasn't going to make laying on the ground. The habitat improvement is worth astronomically more than what he would've paid me for those trees. I have no regrets, and he's never getting any more work out of me.