Check out how low the climber in Nick's photo is keeping his center of gravity. His feet are not on the top center of the branch, they are slightly off to one side.
Here's a photo of my foot position during a branch walk, I'm pretty far out on a long upward sloping limb, totally on the side of the limb. There's no right way to limb walk, every branch is different, I just want you to get the feel for using the opposing force of your TIP and bracing yourself with your legs on one side of the branch to feel more secure. Once you get a sense of it you can stand closer to the top of the branch depending on your rope angle and the unique characteristics of the branch. Keep your center of gravity low, it gives you much more body control.
