Coos bay cut is explained in Berenek's Fundementals of General Treework. The why and how.
With the Coos Bay, you lose directional felling control, which was somewhat predetermined to be lost/ unavailable as it is meant to be used on heavy leaners, which will want to go with the lean and not be so steerable. There is no face cut, only back cuts.
It is like a very, very, very exaggerated kerf/relief cut, with a back cut. The kerf/relief cuts normally put under the face/back cut combo are performed such that the length of the bar and tip point to the fall, with only a shallow cut.
With the bar tip pointing toward the lean, cut deeply toward the center. Maybe good to load it up with wedges, not for forcing it over, just to fill the kerf and reduce any lateral force. Do the same on the other side.
This will result in a strip that is oriented from the direction of the lean, to the opposite direction of the lean. Kinda like a mohawk would look with the direction of the lean being where the mohawk-ed person would be facing.
This mohawk strip is then cut quickly, with a strong and sharp saw from back of the head toward the face.
Berenek also discusses the technique where the back cut wood is shaped into a triangle with one side as the hinge wood, and the other two sides coming to point at the side opposite of the lean. Those two sides are cut though the sides of the hinge a bit, making the hinge narrower.
I believe that this allows the strong and sharp saw to cut through the back cut in less time, leaving the tree with less built up forces within the trunk for a shorter amount of time, resulting in less probability of a barber chair.
Best to see some diagrams, as I'm sure that this explanation is not crystal clear, and a picture speaks a thousand words.