One reason you don't want your back cut high, is if you come in a tad too far you don't have any hinge, and when you drive a wedge in it pushes the trunk forward and it will shoot off the stump forward, and the tree will fall dead backwards. If you bring your back cut in level with your notch, you can physically see how much hinge you have, and the trunk will "hinge" over as it should. If you are just a firewood hack, you should invest $65 in a half inch X 120 foot tag line. Put it as high up as you can get it and put a little tension on it. Then it's "pulling" with the notch, not "pushing" against it. Wedges work, tag lines work better. Wedges have more fails, tag lines have less fails.