Fantastic pictures!
I am no expert on this, but lying down in the undercut of a half felled tree does not strike me as a very clever move.
That notch is to control the direction of the tree when it falls. They still had a lot of cutting to do from the other side. They cut up close to the notch from the other side, it acts like a hinge falling in the direction of the notch.
See how the other two guys are standing on planks, you can see the holes cut for other planks under the notch. That gets them up to where they want to make the cut. You can still find rotting old stumps around here that have those plank holes cut in them.