The other thing that a lot of axe users forget nowadays is that your object is not to hit the wood, it's to separate it. Every stroke that you don't snap out a chip is wasted stroke! Observe; strike; recover. And yeah. 45 degrees from perpendicular is the optimal attack angle. Making a steeper notch wastes less wood I suppose, but that is pretty much never a consideration with an axe. If you want a nice flat end with minimal waste... get a saw.